test: use separate stderr buffers in gitArchive to avoid data race

archive.Stderr and extract.Stderr shared one strings.Builder; os/exec
spawns a stderr-copy goroutine per command, so git archive and tar (which
run concurrently) could write the builder simultaneously. strings.Builder
is not concurrency-safe, so go test -race would flag it on any run where
both processes emit stderr. Give each process its own buffer and report
the relevant one on failure. Flagged by CodeRabbit on PR #1840.

.github/workflows/ci.yml

@@ -47,6 +47,34 @@ jobs:
             exit 1
           fi
 
+  plugin-integration:
+    needs: fast-gate
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@93cb6efe18208431cddfb8368fd83d5badbf9bfd # v5
+        with:
+          persist-credentials: false
+      - uses: actions/setup-go@4a3601121dd01d1626a1e23e37211e3254c1c06c # v6
+        with:
+          go-version-file: go.mod
+      # No fetch_meta: the git-archive clean tree must embed only the
+      # committed meta_data stub (reproduces the bare-module customer state).
+      - name: Run plugin-integration L4 tests
+        run: go test -count=1 -timeout=15m ./tests/plugin_e2e/...
+
+  sidecar-integration:
+    needs: fast-gate
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@93cb6efe18208431cddfb8368fd83d5badbf9bfd # v5
+        with:
+          persist-credentials: false
+      - uses: actions/setup-go@4a3601121dd01d1626a1e23e37211e3254c1c06c # v6
+        with:
+          go-version-file: go.mod
+      - name: Run sidecar tag build + HMAC round-trip
+        run: make sidecar-test
+
   # ── Layer 2: Quality Gate ──────────────────────────────────────────
   unit-test:
     needs: fast-gate
@@ -414,7 +442,7 @@ jobs:
   # ── Results Gate (single required check for branch protection) ─────
   results:
     if: ${{ always() }}
-    needs: [fast-gate, unit-test, lint, script-test, deterministic-gate, coverage, deadcode, e2e-dry-run, e2e-live, security, license-header]
+    needs: [fast-gate, unit-test, lint, script-test, deterministic-gate, coverage, deadcode, e2e-dry-run, e2e-live, security, license-header, plugin-integration, sidecar-integration]
     runs-on: ubuntu-latest
     steps:
       - name: Evaluate results
@@ -434,10 +462,18 @@ jobs:
           echo "| L3 | e2e-live | ${{ needs.e2e-live.result }} |" >> $GITHUB_STEP_SUMMARY
           echo "| L4 | security | ${{ needs.security.result }} |" >> $GITHUB_STEP_SUMMARY
           echo "| L4 | license-header | ${{ needs.license-header.result }} |" >> $GITHUB_STEP_SUMMARY
+          echo "| L4 | plugin-integration (observe-only) | ${{ needs.plugin-integration.result }} |" >> $GITHUB_STEP_SUMMARY
+          echo "| L4 | sidecar-integration (observe-only) | ${{ needs.sidecar-integration.result }} |" >> $GITHUB_STEP_SUMMARY
 
           # Any failure or cancellation in any job blocks the merge.
           # Legitimately skipped jobs (deadcode on push, e2e-live on fork,
           # license-header on push) are OK.
+          #
+          # plugin-integration and sidecar-integration are intentionally NOT
+          # in this loop yet: they run on every PR and their status is shown
+          # in the table above, but a failure is observe-only (non-blocking)
+          # during the initial soak. Add them back here to make them required
+          # once they have proven stable.
           FAILED=0
           for result in \
             "${{ needs.fast-gate.result }}" \

Makefile

@@ -23,7 +23,7 @@ PREFIX   ?= /usr/local
 TEST_GOARCH := $(or $(GOARCH),$(shell go env GOARCH))
 RACE_FLAG := $(if $(filter riscv64,$(TEST_GOARCH)),,-race)
 
-.PHONY: all build vet fmt-check script-test test unit-test integration-test examples-build quality-gate install uninstall clean fetch_meta gitleaks
+.PHONY: all build vet fmt-check script-test test unit-test integration-test examples-build quality-gate install uninstall clean fetch_meta gitleaks sidecar-test
 
 all: test
 
@@ -105,6 +105,14 @@ uninstall:
 clean:
 	rm -f $(BINARY)
 
+# sidecar-test compiles and runs the authsidecar* build-tagged code that the
+# default CI matrix never sees (they carry //go:build tags).
+sidecar-test:
+	go build -tags authsidecar -o /dev/null .
+	go test $(RACE_FLAG) -count=1 -tags authsidecar ./extension/credential/sidecar/ ./extension/transport/sidecar/ ./internal/cmdutil/
+	go test $(RACE_FLAG) -count=1 -tags authsidecar_demo ./sidecar/server-demo/
+	go test $(RACE_FLAG) -count=1 -tags authsidecar ./tests/sidecar_e2e/
+
 # Run secret-leak checks locally before pushing.
 # Step 1: check-doc-tokens catches realistic-looking example tokens in reference
 #         docs and asks you to use _EXAMPLE_TOKEN placeholders instead.

sidecar/server-demo/handler_test.go

@@ -18,6 +18,7 @@ import (
 	"testing"
 
 	extcred "github.com/larksuite/cli/extension/credential"
+	"github.com/larksuite/cli/internal/core"
 	"github.com/larksuite/cli/internal/credential"
 	"github.com/larksuite/cli/internal/envvars"
 	"github.com/larksuite/cli/sidecar"
@@ -585,11 +586,15 @@ func TestProxyHandler_StripsClientSuppliedAuthHeaders(t *testing.T) {
 }
 
 func TestBuildAllowedHosts(t *testing.T) {
-	feishu := struct{ Open, Accounts, MCP string }{
-		"https://open.feishu.cn", "https://accounts.feishu.cn", "https://mcp.feishu.cn",
+	feishu := core.Endpoints{
+		Open:     "https://open.feishu.cn",
+		Accounts: "https://accounts.feishu.cn",
+		MCP:      "https://mcp.feishu.cn",
 	}
-	lark := struct{ Open, Accounts, MCP string }{
-		"https://open.larksuite.com", "https://accounts.larksuite.com", "https://mcp.larksuite.com",
+	lark := core.Endpoints{
+		Open:     "https://open.larksuite.com",
+		Accounts: "https://accounts.larksuite.com",
+		MCP:      "https://mcp.larksuite.com",
 	}
 	hosts := buildAllowedHosts(feishu, lark)
 	// feishu hosts

tests/plugin_e2e/degrade_subsystem_test.go

@@ -0,0 +1,265 @@
+// Copyright (c) 2026 Lark Technologies Pte. Ltd.
+// SPDX-License-Identifier: MIT
+
+package plugin_e2e
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/tidwall/gjson"
+)
+
+// seededCatalogVersion is far newer than the embedded stub's 0.0.0, so the
+// runtime overlay in internal/registry unconditionally applies it.
+const seededCatalogVersion = "9.9.9"
+
+// seededCatalogJSON is a remote_meta.json (registry.MergedRegistry) carrying one
+// obviously-synthetic service. Seeding it into a bare-module fork's on-disk cache
+// gives the runtime catalog real data WITHOUT any network, so a test can prove
+// SchemaCatalog() consults that runtime catalog (issue #1764) rather than the
+// embedded-only (empty stub) catalog. Fields mirror internal/meta.Service.
+const seededCatalogJSON = `{
+  "version": "9.9.9",
+  "services": [
+    {
+      "name": "plugine2e",
+      "version": "v1",
+      "title": "plugin_e2e synthetic service",
+      "description": "synthetic fixture for the runtime-catalog test; not a real API",
+      "servicePath": "/open-apis/plugine2e/v1",
+      "resources": {
+        "widgets": {
+          "methods": {
+            "get": {
+              "id": "plugine2e.widgets.get",
+              "path": "/open-apis/plugine2e/v1/widgets/:id",
+              "httpMethod": "GET",
+              "description": "synthetic read method",
+              "risk": "read",
+              "accessTokens": ["tenant"],
+              "parameters": {
+                "id": {"type": "string", "location": "path", "required": true, "description": "synthetic id"}
+              }
+            }
+          }
+        }
+      }
+    }
+  ]
+}`
+
+// runWithSeededCatalog runs bin against a fresh LARKSUITE_CLI_CONFIG_DIR whose
+// cache already holds cacheJSON as remote_meta.json (plus a fresh, high-version
+// cache-meta so the overlay applies and the TTL never triggers a refetch). Remote
+// meta is left ON so the on-disk cache overlay is consulted, but a long
+// LARKSUITE_CLI_META_TTL keeps the run offline and deterministic. This models a
+// bare-module binary that has runtime metadata available from a warm cache.
+func runWithSeededCatalog(t *testing.T, bin, cacheJSON string, args ...string) result {
+	t.Helper()
+	cfg := t.TempDir()
+	cacheDir := filepath.Join(cfg, "cache")
+	if err := os.MkdirAll(cacheDir, 0o755); err != nil {
+		t.Fatalf("mkdir cache dir: %v", err)
+	}
+	writeFile(t, filepath.Join(cacheDir, "remote_meta.json"), cacheJSON)
+	writeFile(t, filepath.Join(cacheDir, "remote_meta.meta.json"),
+		fmt.Sprintf(`{"last_check_at":%d,"version":%q,"brand":""}`, time.Now().Unix(), seededCatalogVersion))
+	env := append(os.Environ(),
+		"LARKSUITE_CLI_NO_UPDATE_NOTIFIER=1",
+		"LARKSUITE_CLI_NO_SKILLS_NOTIFIER=1",
+		"LARKSUITE_CLI_CONFIG_DIR="+cfg,
+		"LARKSUITE_CLI_META_TTL=1000000",
+	)
+	return runWithEnv(t, bin, env, args...)
+}
+
+// plainPlugin registers a minimal observer-only plugin with NO Restrict rule
+// -- unlike readonly_test.go's plugins, it cannot deny "schema" as
+// out-of-domain, so any failure the command produces below is the command's
+// own behavior against the empty stub catalog, not a policy denial.
+const plainPlugin = `// Code generated by plugin_e2e; DO NOT EDIT.
+package plugin
+
+import (
+	"context"
+
+	"github.com/larksuite/cli/extension/platform"
+)
+
+func init() {
+	platform.Register(
+		platform.NewPlugin("plain", "0.1.0").
+			Observer(platform.After, "noop", platform.All(),
+				func(_ context.Context, _ platform.Invocation) {}).
+			FailOpen().
+			MustBuild())
+}
+`
+
+// TestDegradeStubMetadataSchema pins the #1764 stub-metadata degrade path.
+// The clean tree embeds only the empty meta_data_default.json stub
+// (internal/registry/catalog.go's SchemaCatalog falls through to
+// RuntimeCatalog when EmbeddedServicesTyped() is empty), and run()'s isolated
+// environment disables the remote overlay fetch and points the cache dir at
+// an empty tmp dir, so cmd/schema/schema.go's runSchema sees
+// catalog.Services() == 0 unconditionally -- the exact "offline with a cold
+// cache, remote meta off" branch documented at cmd/schema/schema.go:96-101.
+//
+// Observed real output for both `schema` and `schema im.messages.reply`
+// (identical -- runSchema checks catalog.Services()==0 before parsing args):
+//
+//	exit=2
+//	stdout=(empty)
+//	stderr={"ok":false,"error":{"type":"validation","subtype":"failed_precondition",
+//	  "message":"No API metadata available",
+//	  "hint":"this binary has no embedded API metadata; run any command with
+//	  network access to the open platform once so metadata can be fetched and
+//	  cached"}}
+//
+// This is the PINNED "graceful degrade" criterion: a structured JSON envelope
+// (gjson.Valid, no "panic:" substring) carrying a validation/failed_precondition
+// error with an actionable hint, NOT the raw Go panic crash that
+// install_test.go's TestInstallMustBuildInitPanicCrashesBinary pins for a
+// genuinely broken plugin, and NOT an "Unknown"-shaped internal error.
+// Note: exit==2 alone does not prove "not a crash" -- a genuine Go panic also
+// exits 2. The two real discriminators against a crash are the absence of a
+// "panic:" substring in stderr and stderr being valid JSON (gjson.Valid); both
+// are asserted below.
+func TestDegradeStubMetadataSchema(t *testing.T) {
+	bin := buildFork(t, "plain", plainPlugin)
+	cases := []struct {
+		name string
+		args []string
+	}{
+		{"schema root", []string{"schema"}},
+		{"schema with path", []string{"schema", "im.messages.reply"}},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			res := run(t, bin, tc.args...)
+			t.Logf("exit=%d stdout=%s stderr=%s", res.exit, res.stdout, res.stderr)
+			if res.exit != 2 {
+				t.Fatalf("exit=%d want 2 (graceful validation exit); stdout=%s stderr=%s", res.exit, res.stdout, res.stderr)
+			}
+			if strings.Contains(res.stderr, "panic:") {
+				t.Fatalf("stderr contains a raw Go panic trace, not a graceful degrade; stderr=%s", res.stderr)
+			}
+			if !gjson.Valid(res.stderr) {
+				t.Fatalf("stderr not a structured JSON envelope: %s", res.stderr)
+			}
+			if got := gjson.Get(res.stderr, "error.type").String(); got != "validation" {
+				t.Errorf("error.type=%q want validation", got)
+			}
+			if got := gjson.Get(res.stderr, "error.subtype").String(); got != "failed_precondition" {
+				t.Errorf("error.subtype=%q want failed_precondition", got)
+			}
+			if msg := gjson.Get(res.stderr, "error.message").String(); msg != "No API metadata available" {
+				t.Errorf("error.message=%q want %q", msg, "No API metadata available")
+			}
+			if hint := gjson.Get(res.stderr, "error.hint").String(); !strings.Contains(hint, "no embedded API metadata") {
+				t.Errorf("error.hint=%q want to contain %q", hint, "no embedded API metadata")
+			}
+		})
+	}
+}
+
+// TestRuntimeCatalogResolvesSchema pins the PRIMARY #1764 fix: a bare-module fork
+// (embedded stub only) resolves `schema` against the RUNTIME catalog seeded from
+// the on-disk cache, not the embedded-only catalog. Before f0b6f35f the module
+// build read the embedded-only catalog and returned "Unknown service: <svc>" even
+// though the runtime registry had metadata; after it, registry.SchemaCatalog()
+// falls back to the merged runtime catalog and the lookup succeeds.
+//
+// This is the counterpart to TestDegradeStubMetadataSchema: that test pins the
+// cold-cache corner (no runtime data -> graceful "No API metadata available");
+// this one pins the warm-cache main path (runtime data present -> schema works),
+// so a regression that re-embeds the embedded-only lookup fails HERE with
+// "Unknown service" rather than silently passing.
+func TestRuntimeCatalogResolvesSchema(t *testing.T) {
+	bin := buildFork(t, "plain", plainPlugin)
+	res := runWithSeededCatalog(t, bin, seededCatalogJSON, "schema", "plugine2e")
+	t.Logf("exit=%d stdout=%s stderr=%s", res.exit, res.stdout, res.stderr)
+	out := res.stdout + res.stderr
+	if strings.Contains(out, "Unknown service") {
+		t.Fatalf("schema returned \"Unknown service\" -> runtime catalog NOT consulted (issue #1764 regression); out=%s", out)
+	}
+	if strings.Contains(out, "No API metadata available") {
+		t.Fatalf("schema saw no metadata -> the seeded runtime cache was not loaded; out=%s", out)
+	}
+	if res.exit != 0 {
+		t.Fatalf("exit=%d want 0 (schema resolved from runtime catalog); stdout=%s stderr=%s", res.exit, res.stdout, res.stderr)
+	}
+	if !strings.Contains(out, "plugine2e") {
+		t.Errorf("schema output does not mention the seeded service; out=%s", out)
+	}
+}
+
+// credentialBlockPlugin registers a credential.Provider whose ResolveAccount
+// (and ResolveToken) unconditionally return a *credential.BlockError.
+// internal/credential/credential_provider.go's doResolveAccount returns this
+// error straight from the provider loop -- before any defaultAcct fallback
+// and, transitively, before the LarkClient/HttpClient phases that would issue
+// a real network call ever run (see internal/cmdutil/factory_default.go's
+// Phase 2 -> Phase 4 ordering).
+const credentialBlockPlugin = `// Code generated by plugin_e2e; DO NOT EDIT.
+package plugin
+
+import (
+	"context"
+
+	"github.com/larksuite/cli/extension/credential"
+)
+
+type blockProvider struct{}
+
+func (blockProvider) Name() string { return "block-cred" }
+
+func (blockProvider) ResolveAccount(ctx context.Context) (*credential.Account, error) {
+	return nil, &credential.BlockError{Provider: "block-cred", Reason: "blocked for test"}
+}
+
+func (blockProvider) ResolveToken(ctx context.Context, req credential.TokenSpec) (*credential.Token, error) {
+	return nil, &credential.BlockError{Provider: "block-cred", Reason: "blocked for test"}
+}
+
+func init() {
+	credential.Register(blockProvider{})
+}
+`
+
+// TestSubsystemCredentialBlock pins the credential.BlockError offline effect.
+// Observed real output for `docs +fetch --doc nonexistent`, run twice across
+// separate `go test -count` invocations (byte-identical both times, unlike
+// the transport-abort case -- credential resolution happens once, before any
+// endpoint is chosen, so there is no varying destination URL to leak into the
+// message):
+//
+//	exit=5
+//	stdout=(empty)
+//	stderr={"ok":false,"identity":"bot","error":{"type":"internal","subtype":"unknown",
+//	  "message":"blocked by block-cred: blocked for test"}}
+func TestSubsystemCredentialBlock(t *testing.T) {
+	bin := buildFork(t, "credential-block", credentialBlockPlugin)
+	res := run(t, bin, "docs", "+fetch", "--doc", "nonexistent")
+	t.Logf("exit=%d stdout=%s stderr=%s", res.exit, res.stdout, res.stderr)
+	if res.exit != 5 {
+		t.Fatalf("exit=%d want 5; stdout=%s stderr=%s", res.exit, res.stdout, res.stderr)
+	}
+	if !gjson.Valid(res.stderr) {
+		t.Fatalf("stderr not JSON: %s", res.stderr)
+	}
+	if got := gjson.Get(res.stderr, "error.type").String(); got != "internal" {
+		t.Errorf("error.type=%q want internal", got)
+	}
+	if got := gjson.Get(res.stderr, "error.subtype").String(); got != "unknown" {
+		t.Errorf("error.subtype=%q want unknown", got)
+	}
+	if msg := gjson.Get(res.stderr, "error.message").String(); msg != "blocked by block-cred: blocked for test" {
+		t.Errorf("error.message=%q want %q", msg, "blocked by block-cred: blocked for test")
+	}
+}

tests/plugin_e2e/diagnostics_test.go

@@ -0,0 +1,39 @@
+// Copyright (c) 2026 Lark Technologies Pte. Ltd.
+// SPDX-License-Identifier: MIT
+
+package plugin_e2e
+
+import (
+	"testing"
+
+	"github.com/tidwall/gjson"
+)
+
+// TestDiagnostics asserts the VERIFIED stdout shapes of the two policy/plugin
+// diagnostic commands on a fork carrying the readonly Restrict rule:
+//   - `config policy show`: source_name == the plugin name that installed the
+//     active rule.
+//   - `config plugins show`: {"plugins":[{"name","version","capabilities",...,
+//     "hooks":{...}}],"total":N} with the readonly plugin present.
+func TestDiagnostics(t *testing.T) {
+	bin := buildFork(t, "readonly", readonlyPlugin)
+
+	pol := run(t, bin, "config", "policy", "show")
+	if pol.exit != 0 || !gjson.Valid(pol.stdout) {
+		t.Fatalf("policy show exit=%d stdout=%s stderr=%s", pol.exit, pol.stdout, pol.stderr)
+	}
+	if src := gjson.Get(pol.stdout, "source_name").String(); src != "readonly" {
+		t.Errorf("policy source_name=%q want readonly (stdout=%s)", src, pol.stdout)
+	}
+
+	plug := run(t, bin, "config", "plugins", "show")
+	if plug.exit != 0 || !gjson.Valid(plug.stdout) {
+		t.Fatalf("plugins show exit=%d stdout=%s", plug.exit, plug.stdout)
+	}
+	if total := gjson.Get(plug.stdout, "total").Int(); total < 1 {
+		t.Errorf("plugins total=%d want >=1 (stdout=%s)", total, plug.stdout)
+	}
+	if name := gjson.Get(plug.stdout, "plugins.0.name").String(); name != "readonly" {
+		t.Errorf("plugins.0.name=%q want readonly", name)
+	}
+}

tests/plugin_e2e/harness.go

@@ -0,0 +1,210 @@
+// Copyright (c) 2026 Lark Technologies Pte. Ltd.
+// SPDX-License-Identifier: MIT
+
+// Package plugin_e2e exercises the extension/platform plugin contract the way a
+// real customer does: it builds a fork of lark-cli with a plugin blank-imported,
+// then runs that fork as a subprocess and asserts the real stderr/stdout
+// envelopes and exit codes. This is L4 coverage — the in-process unit and
+// integration tests (extension/..., cmd/...) assert Go error values in the test
+// process and structurally cannot observe envelope serialization, exit codes, or
+// the blank-import -> init -> Register -> InstallAll assembly chain.
+//
+// Mechanism (the "customer build", mirrors xcaddy's build mode):
+//  1. `git archive HEAD` a clean tree containing only committed files (so the
+//     fork embeds the tracked meta_data stub, reproducing the bare-module state).
+//  2. Generate a customer module: go.mod (cli's requires + `replace` to the
+//     archived tree) + go.sum copy + main.go (blank-imports the plugin package)
+//     + plugin package (its init() calls platform.Register).
+//  3. `go build` the fork (offline-capable via the warm module cache), then run
+//     it as a subprocess and assert.
+package plugin_e2e
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"testing"
+	"time"
+)
+
+// cleanTree is the git-archived, committed-only source tree of the repo under
+// test, shared by every fork build. Populated by TestMain (smoke_test.go) —
+// TestMain must live in a _test.go file to be recognized by `go test`, so the
+// entry point sits there while the rest of the harness mechanism lives here.
+var cleanTree string
+
+// baseDir holds the archive tree plus every generated customer module.
+var baseDir string
+
+// repoRoot resolves the lark-cli module root from the test's working directory
+// (which `go test` sets to the package dir, tests/plugin_e2e).
+func repoRoot() (string, error) {
+	out, err := exec.Command("git", "rev-parse", "--show-toplevel").Output()
+	if err != nil {
+		return "", err
+	}
+	return strings.TrimSpace(string(out)), nil
+}
+
+// gitArchive extracts HEAD's committed tree into dst by streaming `git archive`
+// into `tar -x`. Only tracked files are included — gitignored build artifacts
+// (e.g. the fetched meta_data.json) are absent, exactly as a module consumer
+// would see them. It wires the two processes with an explicit pipe rather than a
+// shell, so dst never reaches a shell command line.
+func gitArchive(root, dst string) error {
+	archive := exec.Command("git", "archive", "HEAD")
+	archive.Dir = root
+	extract := exec.Command("tar", "-x", "-C", dst)
+	pipe, err := archive.StdoutPipe()
+	if err != nil {
+		return err
+	}
+	extract.Stdin = pipe
+	// Each process gets its own stderr buffer: os/exec spawns a copy goroutine
+	// per command, so a shared strings.Builder would be written concurrently by
+	// both (git archive and tar run in parallel) -- a data race, since
+	// strings.Builder is not concurrency-safe.
+	var archiveErr, extractErr strings.Builder
+	archive.Stderr = &archiveErr
+	extract.Stderr = &extractErr
+	if err := extract.Start(); err != nil {
+		return err
+	}
+	if err := archive.Run(); err != nil {
+		_ = extract.Wait()
+		return fmt.Errorf("git archive: %w: %s", err, archiveErr.String())
+	}
+	if err := extract.Wait(); err != nil {
+		return fmt.Errorf("tar extract: %w: %s", err, extractErr.String())
+	}
+	return nil
+}
+
+// builtForks caches fork binaries by name so identical forks are built once.
+var builtForks = map[string]string{}
+
+// buildFork generates a customer module whose plugin package body is pluginSrc,
+// builds the fork, and returns the binary path. Forks are cached by name.
+func buildFork(t *testing.T, name, pluginSrc string) string {
+	t.Helper()
+	if bin, ok := builtForks[name]; ok {
+		return bin
+	}
+	mod := filepath.Join(baseDir, "fork-"+name)
+	if err := os.MkdirAll(filepath.Join(mod, "plugin"), 0o755); err != nil {
+		t.Fatalf("mkdir customer module: %v", err)
+	}
+
+	// go.mod: reuse cli's require graph, rename the module, replace cli with the
+	// local archived tree. This avoids `go mod tidy` (no network at test time).
+	rawMod, err := os.ReadFile(filepath.Join(cleanTree, "go.mod"))
+	if err != nil {
+		t.Fatalf("read archived go.mod: %v", err)
+	}
+	gomod := strings.Replace(string(rawMod), "module github.com/larksuite/cli", "module larkcustomer", 1)
+	gomod += "\nrequire github.com/larksuite/cli v0.0.0\n\nreplace github.com/larksuite/cli => " + cleanTree + "\n"
+	writeFile(t, filepath.Join(mod, "go.mod"), gomod)
+
+	// go.sum: transitive dependency hashes are identical to cli's.
+	rawSum, err := os.ReadFile(filepath.Join(cleanTree, "go.sum"))
+	if err != nil {
+		t.Fatalf("read archived go.sum: %v", err)
+	}
+	writeFile(t, filepath.Join(mod, "go.sum"), string(rawSum))
+
+	writeFile(t, filepath.Join(mod, "main.go"), customerMain)
+	writeFile(t, filepath.Join(mod, "plugin", "plugin.go"), pluginSrc)
+
+	bin := filepath.Join(mod, "fork-bin")
+	build := exec.Command("go", "build", "-o", bin, ".")
+	build.Dir = mod
+	// -mod=mod fixes require annotations copied from cli's go.mod; the default
+	// GOPROXY resolves any dep missing from the cache (goproxy in CI/dev).
+	build.Env = append(os.Environ(), "GOFLAGS=-mod=mod")
+	if out, err := build.CombinedOutput(); err != nil {
+		t.Fatalf("build fork %q failed: %v\n%s", name, err, out)
+	}
+	builtForks[name] = bin
+	return bin
+}
+
+const customerMain = `// Code generated by plugin_e2e; DO NOT EDIT.
+package main
+
+import (
+	"os"
+
+	"github.com/larksuite/cli/cmd"
+	_ "larkcustomer/plugin" // blank import triggers plugin init() -> platform.Register
+)
+
+func main() { os.Exit(cmd.Execute()) }
+`
+
+// result is a subprocess run outcome.
+type result struct {
+	stdout string
+	stderr string
+	exit   int
+}
+
+// run executes the fork binary with args in an isolated, offline environment and
+// captures stdout/stderr/exit. Each call gets a fresh empty
+// LARKSUITE_CLI_CONFIG_DIR and LARKSUITE_CLI_REMOTE_META=off, so the fork never
+// inherits the host's ~/.lark-cli cache or makes a startup metadata fetch to the
+// open platform. That reproduces the bare-module customer state (no embedded
+// metadata, cold cache) deterministically on any machine, including CI: without
+// it, whether a command's assertion is reached depends on whether a live network
+// fetch happened to succeed. Tests that need runtime metadata seed it explicitly
+// via runWithSeededCatalog.
+func run(t *testing.T, bin string, args ...string) result {
+	t.Helper()
+	return runWithEnv(t, bin, isolatedEnv(t), args...)
+}
+
+// isolatedEnv is the bare-module, offline environment shared by run() and (as a
+// base) by runWithSeededCatalog.
+func isolatedEnv(t *testing.T) []string {
+	t.Helper()
+	return append(os.Environ(),
+		"LARKSUITE_CLI_NO_UPDATE_NOTIFIER=1",
+		"LARKSUITE_CLI_NO_SKILLS_NOTIFIER=1",
+		"LARKSUITE_CLI_CONFIG_DIR="+t.TempDir(),
+		"LARKSUITE_CLI_REMOTE_META=off",
+	)
+}
+
+// runWithEnv runs bin as a subprocess with the given full environment, capturing
+// stdout/stderr/exit.
+func runWithEnv(t *testing.T, bin string, env []string, args ...string) result {
+	t.Helper()
+	ctx, cancel := context.WithTimeout(context.Background(), 60*time.Second)
+	defer cancel()
+	c := exec.CommandContext(ctx, bin, args...)
+	c.Env = env
+	var stdout, stderr strings.Builder
+	c.Stdout = &stdout
+	c.Stderr = &stderr
+	err := c.Run()
+	exit := 0
+	if err != nil {
+		var ee *exec.ExitError
+		if errors.As(err, &ee) {
+			exit = ee.ExitCode()
+		} else {
+			t.Fatalf("run %v: %v", args, err)
+		}
+	}
+	return result{stdout: stdout.String(), stderr: stderr.String(), exit: exit}
+}
+
+func writeFile(t *testing.T, path, content string) {
+	t.Helper()
+	if err := os.WriteFile(path, []byte(content), 0o644); err != nil {
+		t.Fatalf("write %s: %v", path, err)
+	}
+}

tests/plugin_e2e/install_test.go

@@ -0,0 +1,339 @@
+// Copyright (c) 2026 Lark Technologies Pte. Ltd.
+// SPDX-License-Identifier: MIT
+
+package plugin_e2e
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/tidwall/gjson"
+)
+
+// multipleRestrictPlugin registers TWO distinct plugins that each call
+// Restrict() with an independently valid Rule. cmdpolicy.Resolve rejects
+// more than one distinct Restrict-owner regardless of each rule's own
+// validity (internal/cmdpolicy/resolver.go's distinctOwners check runs
+// before ValidateRule).
+const multipleRestrictPlugin = `// Code generated by plugin_e2e; DO NOT EDIT.
+package plugin
+
+import "github.com/larksuite/cli/extension/platform"
+
+func init() {
+	platform.Register(
+		platform.NewPlugin("restrict-a", "0.1.0").
+			Restrict(&platform.Rule{
+				Name:    "a-rule",
+				Allow:   []string{"docs/**"},
+				MaxRisk: platform.RiskRead,
+			}).
+			MustBuild())
+	platform.Register(
+		platform.NewPlugin("restrict-b", "0.1.0").
+			Restrict(&platform.Rule{
+				Name:    "b-rule",
+				Allow:   []string{"im/**"},
+				MaxRisk: platform.RiskRead,
+			}).
+			MustBuild())
+}
+`
+
+// TestInstallMultipleRestrictPluginsPin pins reason_code=multiple_restrict_plugins.
+// Observed real output (any command, e.g. "schema" -- the fatal guard walks
+// every RunE in the tree so it fires regardless of which command runs):
+//
+//	exit=2
+//	stderr={"ok":false,"error":{"type":"validation","subtype":"failed_precondition",
+//	  "message":"multiple plugins called Restrict; only one plugin may own the
+//	  policy: [restrict-a restrict-b]",
+//	  "hint":"plugin policy configuration is broken (reason_code
+//	  multiple_restrict_plugins); fix the plugin's Restrict rule or remove the
+//	  conflicting plugin"}}
+func TestInstallMultipleRestrictPluginsPin(t *testing.T) {
+	bin := buildFork(t, "multiple-restrict", multipleRestrictPlugin)
+	res := run(t, bin, "schema")
+	t.Logf("exit=%d stdout=%s stderr=%s", res.exit, res.stdout, res.stderr)
+	assertReasonCodeEnvelope(t, res, "multiple_restrict_plugins")
+}
+
+// invalidRulePlugin registers a single plugin whose Restrict Rule carries a
+// syntactically-invalid MaxRisk value. Neither the Builder nor the staging
+// Registrar validate Rule *contents* (only nilness) -- semantic validation
+// happens later, in cmdpolicy.ValidateRule, called from
+// cmd/platform_bootstrap.go's applyUserPolicyPruning -> cmdpolicy.Resolve.
+const invalidRulePlugin = `// Code generated by plugin_e2e; DO NOT EDIT.
+package plugin
+
+import "github.com/larksuite/cli/extension/platform"
+
+func init() {
+	platform.Register(
+		platform.NewPlugin("invalid-rule", "0.1.0").
+			Restrict(&platform.Rule{
+				Name:    "bad-risk",
+				Allow:   []string{"docs/**"},
+				MaxRisk: platform.Risk("bogus"),
+			}).
+			MustBuild())
+}
+`
+
+// TestInstallInvalidRulePin pins reason_code=invalid_rule. Observed real output
+// (schema):
+//
+//	exit=2
+//	stderr={"ok":false,"error":{"type":"validation","subtype":"failed_precondition",
+//	  "message":"plugin \"invalid-rule\" rule invalid: invalid max_risk \"bogus\":
+//	  must be one of read|write|high-risk-write",
+//	  "hint":"plugin policy configuration is broken (reason_code invalid_rule);
+//	  fix the plugin's Restrict rule or remove the conflicting plugin"}}
+func TestInstallInvalidRulePin(t *testing.T) {
+	bin := buildFork(t, "invalid-rule", invalidRulePlugin)
+	res := run(t, bin, "schema")
+	t.Logf("exit=%d stdout=%s stderr=%s", res.exit, res.stdout, res.stderr)
+	assertReasonCodeEnvelope(t, res, "invalid_rule")
+}
+
+// installFailedPlugin is a hand-written bare platform.Plugin (not
+// Builder-based -- Install returning a plain error is not expressible
+// through the Builder's fluent API) whose Install always returns an error.
+// FailurePolicy=FailClosed makes the host abort rather than warn+skip.
+const installFailedPlugin = `// Code generated by plugin_e2e; DO NOT EDIT.
+package plugin
+
+import (
+	"errors"
+
+	"github.com/larksuite/cli/extension/platform"
+)
+
+type installFailed struct{}
+
+func (installFailed) Name() string    { return "install-failed" }
+func (installFailed) Version() string { return "0.1.0" }
+func (installFailed) Capabilities() platform.Capabilities {
+	return platform.Capabilities{FailurePolicy: platform.FailClosed}
+}
+func (installFailed) Install(r platform.Registrar) error {
+	return errors.New("deliberate install failure")
+}
+
+func init() { platform.Register(installFailed{}) }
+`
+
+// TestInstallFailedPin pins reason_code=install_failed. Observed real output
+// (schema):
+//
+//	exit=2
+//	stderr={"ok":false,"error":{"type":"validation","subtype":"failed_precondition",
+//	  "message":"plugin \"install-failed\" (install_failed): Install returned
+//	  error: deliberate install failure",
+//	  "hint":"plugin \"install-failed\" failed to install (reason_code
+//	  install_failed); fix or remove the plugin before running commands"}}
+func TestInstallFailedPin(t *testing.T) {
+	bin := buildFork(t, "install-failed", installFailedPlugin)
+	res := run(t, bin, "schema")
+	t.Logf("exit=%d stdout=%s stderr=%s", res.exit, res.stdout, res.stderr)
+	assertReasonCodeEnvelope(t, res, "install_failed")
+}
+
+// installPanicPlugin is a hand-written bare Plugin whose Install panics.
+// safeCallInstall (internal/platform/host.go) recovers and converts the
+// panic into a typed install_panic error rather than crashing the binary.
+const installPanicPlugin = `// Code generated by plugin_e2e; DO NOT EDIT.
+package plugin
+
+import "github.com/larksuite/cli/extension/platform"
+
+type installPanic struct{}
+
+func (installPanic) Name() string    { return "install-panic" }
+func (installPanic) Version() string { return "0.1.0" }
+func (installPanic) Capabilities() platform.Capabilities {
+	return platform.Capabilities{FailurePolicy: platform.FailClosed}
+}
+func (installPanic) Install(r platform.Registrar) error {
+	panic("deliberate install panic")
+}
+
+func init() { platform.Register(installPanic{}) }
+`
+
+// TestInstallPanicPin pins reason_code=install_panic. Observed real output
+// (schema):
+//
+//	exit=2
+//	stderr={"ok":false,"error":{"type":"validation","subtype":"failed_precondition",
+//	  "message":"plugin \"install-panic\" (install_panic): Install panicked:
+//	  deliberate install panic",
+//	  "hint":"plugin \"install-panic\" failed to install (reason_code
+//	  install_panic); fix or remove the plugin before running commands"}}
+func TestInstallPanicPin(t *testing.T) {
+	bin := buildFork(t, "install-panic", installPanicPlugin)
+	res := run(t, bin, "schema")
+	t.Logf("exit=%d stdout=%s stderr=%s", res.exit, res.stdout, res.stderr)
+	assertReasonCodeEnvelope(t, res, "install_panic")
+}
+
+// pluginNamePanicPlugin is a hand-written bare Plugin whose Name() panics.
+// InstallAll's outer loop calls safeCallName BEFORE it ever reads
+// Capabilities(), so this aborts unconditionally regardless of what
+// Capabilities() would have declared (host.go's isUntrustedConfigError
+// list) -- Capabilities() here is a throwaway zero value, never invoked.
+const pluginNamePanicPlugin = `// Code generated by plugin_e2e; DO NOT EDIT.
+package plugin
+
+import "github.com/larksuite/cli/extension/platform"
+
+type pluginNamePanic struct{}
+
+func (pluginNamePanic) Name() string    { panic("deliberate name panic") }
+func (pluginNamePanic) Version() string { return "0.1.0" }
+func (pluginNamePanic) Capabilities() platform.Capabilities {
+	return platform.Capabilities{}
+}
+func (pluginNamePanic) Install(r platform.Registrar) error { return nil }
+
+func init() { platform.Register(pluginNamePanic{}) }
+`
+
+// TestInstallPluginNamePanicPin pins reason_code=plugin_name_panic. Observed real
+// output (schema):
+//
+//	exit=2
+//	stderr={"ok":false,"error":{"type":"validation","subtype":"failed_precondition",
+//	  "message":"plugin \"<unknown>\" (plugin_name_panic): Plugin.Name()
+//	  panicked: deliberate name panic",
+//	  "hint":"plugin \"<unknown>\" failed to install (reason_code
+//	  plugin_name_panic); fix or remove the plugin before running commands"}}
+func TestInstallPluginNamePanicPin(t *testing.T) {
+	bin := buildFork(t, "plugin-name-panic", pluginNamePanicPlugin)
+	res := run(t, bin, "schema")
+	t.Logf("exit=%d stdout=%s stderr=%s", res.exit, res.stdout, res.stderr)
+	assertReasonCodeEnvelope(t, res, "plugin_name_panic")
+}
+
+// capabilitiesPanicPlugin is a hand-written bare Plugin whose Capabilities()
+// panics. readFailurePolicy (internal/platform/host.go) re-invokes
+// Capabilities() to decide FailOpen vs FailClosed, panics again, and its
+// recover leaves the pre-set FailClosed default in place -- so this aborts
+// unconditionally too, without the plugin ever declaring a real policy.
+const capabilitiesPanicPlugin = `// Code generated by plugin_e2e; DO NOT EDIT.
+package plugin
+
+import "github.com/larksuite/cli/extension/platform"
+
+type capabilitiesPanic struct{}
+
+func (capabilitiesPanic) Name() string    { return "capabilities-panic" }
+func (capabilitiesPanic) Version() string { return "0.1.0" }
+func (capabilitiesPanic) Capabilities() platform.Capabilities {
+	panic("deliberate capabilities panic")
+}
+func (capabilitiesPanic) Install(r platform.Registrar) error { return nil }
+
+func init() { platform.Register(capabilitiesPanic{}) }
+`
+
+// TestInstallCapabilitiesPanicPin pins reason_code=capabilities_panic. Observed
+// real output (schema):
+//
+//	exit=2
+//	stderr={"ok":false,"error":{"type":"validation","subtype":"failed_precondition",
+//	  "message":"plugin \"capabilities-panic\" (capabilities_panic):
+//	  Plugin.Capabilities() panicked: deliberate capabilities panic",
+//	  "hint":"plugin \"capabilities-panic\" failed to install (reason_code
+//	  capabilities_panic); fix or remove the plugin before running commands"}}
+func TestInstallCapabilitiesPanicPin(t *testing.T) {
+	bin := buildFork(t, "capabilities-panic", capabilitiesPanicPlugin)
+	res := run(t, bin, "schema")
+	t.Logf("exit=%d stdout=%s stderr=%s", res.exit, res.stdout, res.stderr)
+	assertReasonCodeEnvelope(t, res, "capabilities_panic")
+}
+
+// restrictsMismatchPlugin is a hand-written bare Plugin that declares
+// Capabilities.Restricts=true (paired with the required FailClosed) but
+// whose Install never calls r.Restrict. stagingRegistrar.validateSelf
+// (internal/platform/staging.go) checks this exact declared-vs-actual
+// consistency after Install returns.
+const restrictsMismatchPlugin = `// Code generated by plugin_e2e; DO NOT EDIT.
+package plugin
+
+import "github.com/larksuite/cli/extension/platform"
+
+type restrictsMismatch struct{}
+
+func (restrictsMismatch) Name() string    { return "restricts-mismatch" }
+func (restrictsMismatch) Version() string { return "0.1.0" }
+func (restrictsMismatch) Capabilities() platform.Capabilities {
+	return platform.Capabilities{Restricts: true, FailurePolicy: platform.FailClosed}
+}
+func (restrictsMismatch) Install(r platform.Registrar) error { return nil }
+
+func init() { platform.Register(restrictsMismatch{}) }
+`
+
+// TestInstallRestrictsMismatchPin pins reason_code=restricts_mismatch.
+// Observed real output (schema):
+//
+//	exit=2
+//	stderr={"ok":false,"error":{"type":"validation","subtype":"failed_precondition",
+//	  "message":"plugin \"restricts-mismatch\" (restricts_mismatch):
+//	  Capabilities.Restricts=true but Install did not call r.Restrict",
+//	  "hint":"plugin \"restricts-mismatch\" failed to install (reason_code
+//	  restricts_mismatch); fix or remove the plugin before running commands"}}
+func TestInstallRestrictsMismatchPin(t *testing.T) {
+	bin := buildFork(t, "restricts-mismatch", restrictsMismatchPlugin)
+	res := run(t, bin, "schema")
+	t.Logf("exit=%d stdout=%s stderr=%s", res.exit, res.stdout, res.stderr)
+	assertReasonCodeEnvelope(t, res, "restricts_mismatch")
+}
+
+// mustBuildPanicPlugin calls MustBuild() on a Builder with an invalid plugin
+// name ("BadName!!" fails ^[a-z0-9][a-z0-9-]*$). This panics from
+// plugin.init(), which runs from the blank-import BEFORE main() has a
+// chance to install any recover-and-envelope guard -- so, unlike every
+// other case here, this crashes the process outright: no JSON envelope,
+// non-zero exit, a raw Go panic trace on stderr.
+const mustBuildPanicPlugin = `// Code generated by plugin_e2e; DO NOT EDIT.
+package plugin
+
+import "github.com/larksuite/cli/extension/platform"
+
+func init() {
+	platform.Register(platform.NewPlugin("BadName!!", "0.1.0").MustBuild())
+}
+`
+
+// TestInstallMustBuildInitPanicCrashesBinary pins the MustBuild init-panic crash
+// shape. This is NOT the plugin_install envelope -- it is a bare Go panic
+// crash, because it happens in init(), before main()'s recover guard
+// exists. Observed real output (schema):
+//
+//	exit=2
+//	stderr=panic: plugin "BadName!!": invalid plugin name "BadName!!": must
+//	  match ^[a-z0-9][a-z0-9-]*$
+//
+//	goroutine 1 [running]:
+//	larkcustomer/plugin.init.0(...)
+//	        .../plugin/plugin.go:7
+//	...
+func TestInstallMustBuildInitPanicCrashesBinary(t *testing.T) {
+	bin := buildFork(t, "mustbuild-panic", mustBuildPanicPlugin)
+	res := run(t, bin, "schema")
+	t.Logf("exit=%d stdout=%s stderr=%s", res.exit, res.stdout, res.stderr)
+	if res.exit == 0 {
+		t.Fatalf("expected non-zero exit on init panic; exit=%d stdout=%s stderr=%s", res.exit, res.stdout, res.stderr)
+	}
+	if gjson.Valid(res.stderr) {
+		t.Fatalf("expected a raw panic trace, not a JSON envelope; stderr=%s", res.stderr)
+	}
+	if !strings.Contains(res.stderr, "panic:") {
+		t.Fatalf("stderr missing Go panic trace; stderr=%s", res.stderr)
+	}
+	if !strings.Contains(res.stderr, `invalid plugin name "BadName!!"`) {
+		t.Errorf("stderr missing the Builder's invalid-name message; stderr=%s", res.stderr)
+	}
+}

tests/plugin_e2e/observe_wrap_test.go

@@ -0,0 +1,298 @@
+// Copyright (c) 2026 Lark Technologies Pte. Ltd.
+// SPDX-License-Identifier: MIT
+
+package plugin_e2e
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/tidwall/gjson"
+)
+
+// auditPlugin registers a single After observer matching every command that
+// logs "[audit] <path>" to stderr. Based on (a simplified form of) the
+// shipped extension/platform/examples/audit-observer example.
+const auditPlugin = `// Code generated by plugin_e2e; DO NOT EDIT.
+package plugin
+
+import (
+	"context"
+	"fmt"
+	"os"
+
+	"github.com/larksuite/cli/extension/platform"
+)
+
+func init() {
+	platform.Register(
+		platform.NewPlugin("audit", "0.1.0").
+			Observer(platform.After, "log", platform.All(),
+				func(_ context.Context, inv platform.Invocation) {
+					fmt.Fprintf(os.Stderr, "[audit] %s\n", inv.Cmd().Path())
+				}).
+			FailOpen().
+			MustBuild())
+}
+`
+
+// TestObservePin pins the audit observer's stderr line format. Observed
+// real output (docs +fetch --doc nonexistent, a real read-risk command that
+// fails downstream with an API error unrelated to the plugin):
+//
+//	exit=1
+//	stderr=[audit] docs/+fetch
+//	{"ok":false,"identity":"user","error":{"type":"api","subtype":"unknown",...}}
+//
+// The observer line always leads, on its own line, before whatever the
+// command itself writes to stderr.
+func TestObservePin(t *testing.T) {
+	bin := buildFork(t, "audit", auditPlugin)
+	res := run(t, bin, "docs", "+fetch", "--doc", "nonexistent")
+	if !strings.Contains(res.stderr, "[audit] docs/+fetch\n") {
+		t.Fatalf("stderr missing audit line; stderr=%s", res.stderr)
+	}
+}
+
+// auditRestrictPlugin combines an After observer with a Restrict rule in one
+// plugin, so a denied command's stderr carries both the observer's
+// side-effect and the denial envelope: the framework's contract is that
+// After observers fire even for denied commands (see
+// extension/platform/invocation.go's DeniedByPolicy doc).
+const auditRestrictPlugin = `// Code generated by plugin_e2e; DO NOT EDIT.
+package plugin
+
+import (
+	"context"
+	"fmt"
+	"os"
+
+	"github.com/larksuite/cli/extension/platform"
+)
+
+func init() {
+	platform.Register(
+		platform.NewPlugin("audit-restrict", "0.1.0").
+			Observer(platform.After, "log", platform.All(),
+				func(_ context.Context, inv platform.Invocation) {
+					fmt.Fprintf(os.Stderr, "[audit] %s\n", inv.Cmd().Path())
+				}).
+			Restrict(&platform.Rule{
+				Name:    "agent-readonly",
+				Allow:   []string{"docs/**", "im/**"},
+				MaxRisk: platform.RiskRead,
+			}).
+			MustBuild())
+}
+`
+
+// TestObserveOnDeniedPin pins the audit-contract case: a denied command's
+// stderr carries BOTH the observer's audit line AND the denial envelope,
+// concatenated in a single stream, audit line first. Observed real output
+// (docs +update --doc-token x --content y, denied write_not_allowed):
+//
+//	exit=2
+//	stderr=[audit] docs/+update
+//	{"ok":false,"error":{"type":"validation","subtype":"failed_precondition",...}}
+//
+// The leading "[audit] ..." line means gjson.Valid on the raw stderr is
+// false; the JSON envelope must be sliced out from the first '{' before
+// parsing it as JSON.
+func TestObserveOnDeniedPin(t *testing.T) {
+	bin := buildFork(t, "audit-restrict", auditRestrictPlugin)
+	res := run(t, bin, "docs", "+update", "--doc-token", "x", "--content", "y")
+	if res.exit != 2 {
+		t.Fatalf("exit=%d stdout=%s stderr=%s", res.exit, res.stdout, res.stderr)
+	}
+	if !strings.Contains(res.stderr, "[audit] docs/+update\n") {
+		t.Fatalf("stderr missing audit line on a denied command; stderr=%s", res.stderr)
+	}
+	i := strings.Index(res.stderr, "{")
+	if i < 0 {
+		t.Fatalf("stderr has no JSON envelope after the audit line; stderr=%s", res.stderr)
+	}
+	envelope := res.stderr[i:]
+	if !gjson.Valid(envelope) {
+		t.Fatalf("sliced envelope not JSON: %s", envelope)
+	}
+	if got := gjson.Get(envelope, "error.type").String(); got != "validation" {
+		t.Errorf("error.type=%q want validation", got)
+	}
+	if got := gjson.Get(envelope, "error.subtype").String(); got != "failed_precondition" {
+		t.Errorf("error.subtype=%q want failed_precondition", got)
+	}
+	if hint := gjson.Get(envelope, "error.hint").String(); !strings.Contains(hint, "reason_code write_not_allowed") {
+		t.Errorf("hint=%q want to contain reason_code write_not_allowed", hint)
+	}
+}
+
+// observerPanicPlugin's After observer panics unconditionally. runObserverSafe
+// (internal/hook/install.go) must isolate the panic so command dispatch
+// still completes normally.
+const observerPanicPlugin = `// Code generated by plugin_e2e; DO NOT EDIT.
+package plugin
+
+import (
+	"context"
+
+	"github.com/larksuite/cli/extension/platform"
+)
+
+func init() {
+	platform.Register(
+		platform.NewPlugin("observer-panic", "0.1.0").
+			Observer(platform.After, "log", platform.All(),
+				func(_ context.Context, _ platform.Invocation) {
+					panic("boom")
+				}).
+			FailOpen().
+			MustBuild())
+}
+`
+
+// TestObserverPanicIsolationPin pins panic isolation: an After observer that
+// always panics must not affect the command's own outcome. The assertion is
+// baseline-relative -- the panicking-observer fork's exit code must equal the
+// noop-observer baseline fork's for the same `schema` command (a local,
+// network-free, read-risk command), whatever that shared exit code is.
+// Observed real output at pin time:
+//
+//	panicking: exit=0 stderr=warning: hook "observer-panic.log" panicked: boom
+//	baseline:  exit=0 stderr=(empty)
+//
+// The panic is fully swallowed by runObserverSafe (internal/hook/install.go),
+// surfacing only as a stderr warning line, never as a non-zero exit or crash.
+func TestObserverPanicIsolationPin(t *testing.T) {
+	bin := buildFork(t, "observer-panic", observerPanicPlugin)
+	res := run(t, bin, "schema")
+
+	baselineBin := buildFork(t, "smoke", noopPlugin)
+	baseline := run(t, baselineBin, "schema")
+
+	if res.exit != baseline.exit {
+		t.Fatalf("panicking-observer exit=%d differs from baseline exit=%d; stderr=%s", res.exit, baseline.exit, res.stderr)
+	}
+	if !strings.Contains(res.stderr, `warning: hook "observer-panic.log" panicked: boom`) {
+		t.Errorf("stderr missing panic-isolation warning; stderr=%s", res.stderr)
+	}
+}
+
+// wrapAbortPlugin's Wrapper short-circuits every command with an AbortError
+// instead of calling next.
+const wrapAbortPlugin = `// Code generated by plugin_e2e; DO NOT EDIT.
+package plugin
+
+import (
+	"context"
+
+	"github.com/larksuite/cli/extension/platform"
+)
+
+func init() {
+	platform.Register(
+		platform.NewPlugin("wrap-abort", "0.1.0").
+			Wrap("guard", platform.All(), func(next platform.Handler) platform.Handler {
+				return func(ctx context.Context, inv platform.Invocation) error {
+					return &platform.AbortError{
+						HookName: "guard",
+						Reason:   "blocked for test",
+					}
+				}
+			}).
+			FailOpen().
+			MustBuild())
+}
+`
+
+// TestWrapAbortPin pins the wrap-abort envelope shape. An *AbortError
+// returned by a Wrapper is converted by wrapAbortError
+// (internal/hook/install.go) into the SAME envelope shape as a Restrict
+// denial -- error.type=="validation", error.subtype=="failed_precondition"
+// -- NOT a distinct "hook" error type. Observed real output (docs +fetch
+// --doc nonexistent, wrapper aborts unconditionally before calling next):
+//
+//	exit=2
+//	stderr={"ok":false,"error":{"type":"validation","subtype":"failed_precondition",
+//	  "message":"hook \"wrap-abort.guard\" aborted: blocked for test",
+//	  "hint":"plugin hook \"wrap-abort.guard\" aborted this command; adjust the
+//	  request to satisfy the hook's policy, or remove the plugin"}}
+//
+// HookName is namespaced to "<plugin-name>.<hookName>" ("wrap-abort.guard")
+// regardless of the HookName the plugin set on the AbortError itself
+// (namespacedWrap overwrites it) -- see internal/hook/install.go.
+func TestWrapAbortPin(t *testing.T) {
+	bin := buildFork(t, "wrap-abort", wrapAbortPlugin)
+	res := run(t, bin, "docs", "+fetch", "--doc", "nonexistent")
+	if res.exit != 2 {
+		t.Fatalf("exit=%d stdout=%s stderr=%s", res.exit, res.stdout, res.stderr)
+	}
+	if !gjson.Valid(res.stderr) {
+		t.Fatalf("stderr not JSON: %s", res.stderr)
+	}
+	if got := gjson.Get(res.stderr, "error.type").String(); got != "validation" {
+		t.Errorf("error.type=%q want validation", got)
+	}
+	if got := gjson.Get(res.stderr, "error.subtype").String(); got != "failed_precondition" {
+		t.Errorf("error.subtype=%q want failed_precondition", got)
+	}
+	if msg := gjson.Get(res.stderr, "error.message").String(); !strings.Contains(msg, `hook "wrap-abort.guard" aborted: blocked for test`) {
+		t.Errorf("error.message=%q want to contain the namespaced hook name and Reason", msg)
+	}
+	if hint := gjson.Get(res.stderr, "error.hint").String(); !strings.Contains(hint, `plugin hook "wrap-abort.guard" aborted this command`) {
+		t.Errorf("error.hint=%q want to contain the abort hint", hint)
+	}
+}
+
+// wrapPanicPlugin's Wrapper factory panics on every invocation (the factory
+// closure itself, not the returned Handler).
+const wrapPanicPlugin = `// Code generated by plugin_e2e; DO NOT EDIT.
+package plugin
+
+import (
+	"github.com/larksuite/cli/extension/platform"
+)
+
+func init() {
+	platform.Register(
+		platform.NewPlugin("wrap-panic", "0.1.0").
+			Wrap("guard", platform.All(), func(next platform.Handler) platform.Handler {
+				panic("wrap boom")
+			}).
+			FailOpen().
+			MustBuild())
+}
+`
+
+// TestWrapPanicPin pins the wrap-panic envelope shape: a panicking Wrapper
+// factory does not crash the process. recoverWrap (internal/hook/install.go)
+// converts the panic into the same validation/failed_precondition shape as
+// wrap-abort, with a distinct message/hint pair. Observed real output (docs
+// +fetch --doc nonexistent, wrapper factory panics unconditionally):
+//
+//	exit=2
+//	stderr={"ok":false,"error":{"type":"validation","subtype":"failed_precondition",
+//	  "message":"hook \"wrap-panic.guard\" panicked: wrap boom",
+//	  "hint":"plugin hook \"wrap-panic.guard\" crashed while handling this
+//	  command; report the panic to the plugin author or remove the plugin"}}
+func TestWrapPanicPin(t *testing.T) {
+	bin := buildFork(t, "wrap-panic", wrapPanicPlugin)
+	res := run(t, bin, "docs", "+fetch", "--doc", "nonexistent")
+	if res.exit != 2 {
+		t.Fatalf("exit=%d stdout=%s stderr=%s", res.exit, res.stdout, res.stderr)
+	}
+	if !gjson.Valid(res.stderr) {
+		t.Fatalf("stderr not JSON: %s", res.stderr)
+	}
+	if got := gjson.Get(res.stderr, "error.type").String(); got != "validation" {
+		t.Errorf("error.type=%q want validation", got)
+	}
+	if got := gjson.Get(res.stderr, "error.subtype").String(); got != "failed_precondition" {
+		t.Errorf("error.subtype=%q want failed_precondition", got)
+	}
+	if msg := gjson.Get(res.stderr, "error.message").String(); !strings.Contains(msg, `hook "wrap-panic.guard" panicked: wrap boom`) {
+		t.Errorf("error.message=%q want to contain the namespaced hook name and panic value", msg)
+	}
+	if hint := gjson.Get(res.stderr, "error.hint").String(); !strings.Contains(hint, `plugin hook "wrap-panic.guard" crashed while handling this command`) {
+		t.Errorf("error.hint=%q want to contain the panic hint", hint)
+	}
+}

tests/plugin_e2e/restrict_test.go

@@ -0,0 +1,205 @@
+// Copyright (c) 2026 Lark Technologies Pte. Ltd.
+// SPDX-License-Identifier: MIT
+
+package plugin_e2e
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/tidwall/gjson"
+)
+
+// readonlyPlugin registers a Restrict rule that only allows read-risk
+// commands under the docs/** and im/** domains. It mirrors the official
+// example readonly-policy configuration.
+const readonlyPlugin = `// Code generated by plugin_e2e; DO NOT EDIT.
+package plugin
+
+import "github.com/larksuite/cli/extension/platform"
+
+func init() {
+	platform.Register(
+		platform.NewPlugin("readonly", "0.1.0").
+			Restrict(&platform.Rule{
+				Name:    "agent-readonly",
+				Allow:   []string{"docs/**", "im/**"},
+				MaxRisk: platform.RiskRead,
+			}).
+			MustBuild())
+}
+`
+
+// TestReadonlyDenial asserts the VERIFIED denial envelope shape: stderr is
+// valid JSON, error.type=="validation", error.subtype=="failed_precondition",
+// error.hint contains the literal "reason_code <X>" substring, and the
+// process exits 2. reason_code lives only in the hint string, not a
+// structured field.
+func TestReadonlyDenial(t *testing.T) {
+	bin := buildFork(t, "readonly", readonlyPlugin)
+	// Note: reason_code mixed_children_policy is intentionally NOT covered here.
+	// It requires a parent command whose *enumerated children* have mixed
+	// allow/deny outcomes, which needs the full command tree from API metadata.
+	// This L4 harness builds a bare-module fork (embedded stub only), so offline
+	// a parent like "sheets" has no known children and collapses to
+	// domain_not_allowed -- identical to the "leaf out of allow list" case and
+	// not a distinct reason_code. Covered instead by the in-process cmdpolicy
+	// unit tests, which construct a mixed-children tree directly.
+	cases := []struct {
+		name       string
+		args       []string
+		reasonCode string
+	}{
+		{"write in allowed domain", []string{"docs", "+update", "--doc-token", "x", "--content", "y"}, "write_not_allowed"},
+		{"leaf out of allow list", []string{"schema"}, "domain_not_allowed"},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			assertReasonCodeEnvelope(t, run(t, bin, tc.args...), tc.reasonCode)
+		})
+	}
+}
+
+// TestReadonlyAllows asserts the allow-path: a read command inside an
+// allowed domain must NOT be denied by the policy gate. It may still fail
+// downstream (e.g. api/auth error), but that failure must not carry the
+// denial envelope shape and must not exit 2.
+func TestReadonlyAllows(t *testing.T) {
+	bin := buildFork(t, "readonly", readonlyPlugin)
+	res := run(t, bin, "docs", "+fetch", "--doc", "nonexistent")
+	if res.exit == 2 {
+		t.Fatalf("read command was denied (exit=2); stderr=%s", res.stderr)
+	}
+	if gjson.Valid(res.stderr) && gjson.Get(res.stderr, "error.subtype").String() == "failed_precondition" {
+		t.Errorf("read command produced a denial envelope; stderr=%s", res.stderr)
+	}
+}
+
+// identityPlugin registers a Restrict rule scoped to bot identities only.
+// im +messages-search declares AuthTypes:["user"] (see
+// shortcuts/im/im_messages_search.go), so it has no intersection with the
+// rule's bot-only whitelist regardless of which --as value the caller
+// passes: platform.Rule.Identities is checked against the command's own
+// static supported-identities annotation, not the runtime --as flag.
+const identityPlugin = `// Code generated by plugin_e2e; DO NOT EDIT.
+package plugin
+
+import "github.com/larksuite/cli/extension/platform"
+
+func init() {
+	platform.Register(
+		platform.NewPlugin("identity-restrict", "0.1.0").
+			Restrict(&platform.Rule{
+				Name:       "bot-only",
+				Allow:      []string{"im/**"},
+				MaxRisk:    platform.RiskRead,
+				Identities: []platform.Identity{platform.IdentityBot},
+			}).
+			MustBuild())
+}
+`
+
+// denylistPlugin registers a Restrict rule that allows the docs/** domain
+// but explicitly denies docs/+search (a real read-risk leaf, see
+// shortcuts/doc/docs_search.go). Deny has priority over Allow, so the
+// command is rejected before MaxRisk is even consulted.
+const denylistPlugin = `// Code generated by plugin_e2e; DO NOT EDIT.
+package plugin
+
+import "github.com/larksuite/cli/extension/platform"
+
+func init() {
+	platform.Register(
+		platform.NewPlugin("denylist-restrict", "0.1.0").
+			Restrict(&platform.Rule{
+				Name:    "deny-search",
+				Allow:   []string{"docs/**"},
+				Deny:    []string{"docs/+search"},
+				MaxRisk: platform.RiskRead,
+			}).
+			MustBuild())
+}
+`
+
+// multiRulePlugin registers two scope-exclusive Restrict rules (im-only,
+// docs-only). A command outside both domains (e.g. the top-level "schema"
+// command, itself read-risk and already proven to hit domain_not_allowed
+// under a single Allow:["docs/**","im/**"] rule in TestReadonlyDenial) is
+// rejected by both rules, so cmdpolicy's OR-engine collapses the two
+// per-rule denials into the aggregate reason_code "no_matching_rule".
+const multiRulePlugin = `// Code generated by plugin_e2e; DO NOT EDIT.
+package plugin
+
+import "github.com/larksuite/cli/extension/platform"
+
+func init() {
+	platform.Register(
+		platform.NewPlugin("multi-rule-restrict", "0.1.0").
+			Restrict(&platform.Rule{
+				Name:    "im-only",
+				Allow:   []string{"im/**"},
+				MaxRisk: platform.RiskRead,
+			}).
+			Restrict(&platform.Rule{
+				Name:    "docs-only",
+				Allow:   []string{"docs/**"},
+				MaxRisk: platform.RiskRead,
+			}).
+			MustBuild())
+}
+`
+
+// assertReasonCodeEnvelope asserts the VERIFIED envelope shape shared by every
+// reason_code across this package -- both policy denials (this file) and
+// install-time failures (install_test.go): exit 2, valid JSON on stderr,
+// error.type=="validation", error.subtype=="failed_precondition", and
+// error.hint containing "reason_code <wantReasonCode>". Both paths render
+// through the SAME cmd/platform_guards.go WithHint(...) family, embedding
+// reason_code in the hint STRING, not a structured error.detail.reason_code
+// field (contradicting internal/platform/error.go:34's comment).
+func assertReasonCodeEnvelope(t *testing.T, res result, wantReasonCode string) {
+	t.Helper()
+	if res.exit != 2 {
+		t.Fatalf("exit=%d stdout=%s stderr=%s", res.exit, res.stdout, res.stderr)
+	}
+	if !gjson.Valid(res.stderr) {
+		t.Fatalf("stderr not JSON: %s", res.stderr)
+	}
+	if got := gjson.Get(res.stderr, "error.type").String(); got != "validation" {
+		t.Errorf("error.type=%q want validation", got)
+	}
+	if got := gjson.Get(res.stderr, "error.subtype").String(); got != "failed_precondition" {
+		t.Errorf("error.subtype=%q want failed_precondition", got)
+	}
+	if hint := gjson.Get(res.stderr, "error.hint").String(); !strings.Contains(hint, "reason_code "+wantReasonCode) {
+		t.Errorf("hint=%q want to contain reason_code %s", hint, wantReasonCode)
+	}
+}
+
+// TestIdentityMismatchDenial pins reason_code=identity_mismatch: a bot-only
+// rule rejects a command whose declared AuthTypes don't include "bot".
+func TestIdentityMismatchDenial(t *testing.T) {
+	bin := buildFork(t, "identity", identityPlugin)
+	res := run(t, bin, "im", "+messages-search", "--as", "user")
+	t.Logf("exit=%d stdout=%s stderr=%s", res.exit, res.stdout, res.stderr)
+	assertReasonCodeEnvelope(t, res, "identity_mismatch")
+}
+
+// TestDenylistDenial pins reason_code=command_denylisted: a Deny glob hit
+// rejects the command even though it also matches Allow.
+func TestDenylistDenial(t *testing.T) {
+	bin := buildFork(t, "denylist", denylistPlugin)
+	res := run(t, bin, "docs", "+search")
+	t.Logf("exit=%d stdout=%s stderr=%s", res.exit, res.stdout, res.stderr)
+	assertReasonCodeEnvelope(t, res, "command_denylisted")
+}
+
+// TestMultiRuleDenial pins reason_code=no_matching_rule: a command rejected
+// by every rule in a multi-Restrict() plugin gets the aggregate reason_code,
+// not either rule's own per-rule reason_code.
+func TestMultiRuleDenial(t *testing.T) {
+	bin := buildFork(t, "multirule", multiRulePlugin)
+	res := run(t, bin, "schema")
+	t.Logf("exit=%d stdout=%s stderr=%s", res.exit, res.stdout, res.stderr)
+	assertReasonCodeEnvelope(t, res, "no_matching_rule")
+}

tests/plugin_e2e/smoke_test.go

@@ -0,0 +1,69 @@
+// Copyright (c) 2026 Lark Technologies Pte. Ltd.
+// SPDX-License-Identifier: MIT
+
+package plugin_e2e
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+// TestMain archives HEAD's committed tree once for the whole package before
+// any fork build runs. It lives here (not in harness.go) because `go test`
+// only discovers TestMain in a _test.go file — a TestMain defined in a plain
+// .go file is silently never invoked.
+// NOTE: exactly one TestMain is allowed per package — do not add another in other _test.go files here.
+func TestMain(m *testing.M) {
+	root, err := repoRoot()
+	if err != nil {
+		panic("locate repo root: " + err.Error())
+	}
+	baseDir, err = os.MkdirTemp("", "plugin-e2e-")
+	if err != nil {
+		panic("mkdtemp: " + err.Error())
+	}
+	cleanTree = filepath.Join(baseDir, "larkcli-clean")
+	if err := os.MkdirAll(cleanTree, 0o755); err != nil {
+		panic("mkdir clean tree: " + err.Error())
+	}
+	if err := gitArchive(root, cleanTree); err != nil {
+		panic("git archive: " + err.Error())
+	}
+	code := m.Run()
+	_ = os.RemoveAll(baseDir)
+	os.Exit(code)
+}
+
+// noopPlugin registers a plugin that installs nothing observable, proving
+// the blank-import -> init -> Register -> InstallAll assembly chain links
+// and the fork boots.
+const noopPlugin = `// Code generated by plugin_e2e; DO NOT EDIT.
+package plugin
+
+import (
+	"context"
+
+	"github.com/larksuite/cli/extension/platform"
+)
+
+func init() {
+	platform.Register(
+		platform.NewPlugin("smoke", "0.0.1").
+			Observer(platform.After, "noop", platform.All(),
+				func(_ context.Context, _ platform.Invocation) {}).
+			FailOpen().
+			MustBuild())
+}
+`
+
+func TestSmokeForkBoots(t *testing.T) {
+	bin := buildFork(t, "smoke", noopPlugin)
+	res := run(t, bin, "--help")
+	if res.exit != 0 {
+		t.Fatalf("--help exit=%d stderr=%s", res.exit, res.stderr)
+	}
+	if res.stdout == "" {
+		t.Fatalf("--help produced empty stdout")
+	}
+}

tests/sidecar_e2e/roundtrip_test.go

@@ -0,0 +1,466 @@
+// Copyright (c) 2026 Lark Technologies Pte. Ltd.
+// SPDX-License-Identifier: MIT
+
+//go:build authsidecar
+
+// Package sidecar_e2e proves the sidecar auth-proxy wire protocol end-to-end,
+// offline and secret-free: a real fork binary (built with -tags authsidecar,
+// exercising the REAL extension/transport/sidecar interceptor) signs a
+// request with HMAC-SHA256 and routes it to an in-test sidecar, which
+// verifies the signature using the REAL sidecar.Verify / sidecar.CanonicalRequest
+// from github.com/larksuite/cli/sidecar, injects a synthetic token, and
+// forwards to an in-test mock upstream.
+//
+// DEVIATION FROM THE ORIGINAL PLAN: the plan called for driving the real
+// sidecar/server-demo binary (built with -tags authsidecar_demo) as the
+// middle process. That is infeasible for an OFFLINE test, for three
+// independent reasons, all verified in source:
+//
+//  1. sidecar/server-demo/handler.go:171 resolves a REAL token via
+//     h.cred.ResolveToken(...), which errors out unless the machine has run
+//     `lark-cli auth login` — there is no way to make it return a token
+//     without live credentials.
+//  2. sidecar/server-demo/main.go builds handler.allowedHosts from
+//     core.ResolveEndpoints(BrandFeishu/BrandLark) only — real feishu/lark
+//     hosts. An in-test mock (127.0.0.1:<port>) is never in that allowlist
+//     and would be rejected with 403 (handler.go step 4).
+//  3. sidecar/server-demo/handler.go:184 pins the forward scheme to
+//     "https://" + targetHost, ignoring the client-supplied scheme. It can
+//     never be redirected to an http:// mock.
+//
+// server-demo's verify+inject logic is ALREADY covered by
+// `go test -tags authsidecar_demo ./sidecar/server-demo/` (see the
+// sidecar-test Makefile target, item 3) — that is unit-level coverage of the
+// same code paths this file would otherwise exercise via a real subprocess.
+//
+// So instead, this test builds its OWN in-test sidecar (an httptest.Server)
+// that mirrors server-demo/handler.go's verify+inject steps 0-8 exactly,
+// using the real protocol package (sidecar.Verify, sidecar.CanonicalRequest,
+// sidecar.BodySHA256, the Header* / Sentinel* / Identity* constants) — the
+// same symbols server-demo itself uses. This is the standard shape for this
+// kind of test: one real external process (the fork binary, compiled with
+// the production interceptor code) plus two in-process httptest.Server
+// stand-ins (sidecar, upstream). It proves the real wire protocol end-to-end
+// without requiring live credentials, real feishu/lark hosts, or TLS.
+//
+// Every key/token/app-id here is an obviously-synthetic placeholder; nothing
+// in this file can authenticate against anything real.
+package sidecar_e2e
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/larksuite/cli/sidecar"
+)
+
+// Synthetic, obviously-fake fixtures. None of these are real secrets.
+const (
+	testProxyKey  = "test-proxy-key-not-a-real-secret-000000000000"
+	testAppID     = "cli_test_app_not_real"
+	injectedToken = "fake-injected-token-not-real"
+)
+
+// TestSidecarHMACRoundTrip drives the whole wire protocol as three named
+// steps so the flow is readable at a glance; each step's mechanics live in a
+// dedicated helper below.
+func TestSidecarHMACRoundTrip(t *testing.T) {
+	// Two in-process stand-ins: the mock upstream (for open.feishu.cn) and the
+	// in-test sidecar (server-demo's verify+inject, via the real protocol pkg).
+	upstream := startMockUpstream(t)
+	sc := startInTestSidecar(t, []byte(testProxyKey), upstream.URL)
+
+	// One real external process: lark-cli built with -tags authsidecar, run
+	// fully offline against the in-test sidecar.
+	bin := buildAuthsidecarFork(t)
+	runFork(t, bin, sc.URL)
+
+	// Assert the three properties of a correct round trip.
+	assertInterceptorSigned(t, sc)                  // (a)+(c) fork -> sidecar
+	assertInjectedTokenReachedUpstream(t, upstream) // (b)     sidecar -> upstream
+}
+
+// --- request capture -------------------------------------------------------
+
+// capturedRequest snapshots the parts of an *http.Request that matter for
+// assertions, taken before the request (and its body reader) is consumed or
+// goes out of scope.
+type capturedRequest struct {
+	method  string
+	path    string
+	headers http.Header
+	body    []byte
+}
+
+// requestSink stores the request a stub server saw, guarded so the httptest
+// handler goroutine and the test goroutine can hand it over safely.
+type requestSink struct {
+	mu  sync.Mutex
+	req *capturedRequest
+}
+
+func (s *requestSink) capture(r *http.Request, body []byte) {
+	snap := capturedRequest{
+		method:  r.Method,
+		path:    r.URL.RequestURI(),
+		headers: r.Header.Clone(),
+		body:    body,
+	}
+	s.mu.Lock()
+	s.req = &snap
+	s.mu.Unlock()
+}
+
+func (s *requestSink) get() *capturedRequest {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	return s.req
+}
+
+// --- mock upstream (stands in for open.feishu.cn) --------------------------
+
+type mockUpstream struct {
+	*httptest.Server
+	sink requestSink
+}
+
+func startMockUpstream(t *testing.T) *mockUpstream {
+	t.Helper()
+	m := &mockUpstream{}
+	m.Server = httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		body, _ := io.ReadAll(r.Body)
+		m.sink.capture(r, body)
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(http.StatusOK)
+		_, _ = w.Write([]byte(`{"code":0,"msg":"success","data":{"document":{"content":"mock content"}}}`))
+	}))
+	t.Cleanup(m.Close)
+	return m
+}
+
+// --- in-test sidecar (mirrors server-demo/handler.go verify+inject) --------
+
+type inTestSidecar struct {
+	*httptest.Server
+	key         []byte
+	upstreamURL string
+	sink        requestSink
+
+	mu        sync.Mutex // guards verifyRan/verifyErr
+	verifyRan bool
+	verifyErr error
+}
+
+func startInTestSidecar(t *testing.T, key []byte, upstreamURL string) *inTestSidecar {
+	t.Helper()
+	s := &inTestSidecar{key: key, upstreamURL: upstreamURL}
+	s.Server = httptest.NewServer(http.HandlerFunc(s.handle))
+	t.Cleanup(s.Close)
+	return s
+}
+
+// handle is the request flow: capture -> verify (steps 0-4) -> inject+forward.
+func (s *inTestSidecar) handle(w http.ResponseWriter, r *http.Request) {
+	body, _ := io.ReadAll(r.Body)
+	s.sink.capture(r, body)
+
+	authHeader, ok := s.verifyProxyRequest(w, r, body)
+	if !ok {
+		return
+	}
+	s.forwardWithInjectedToken(w, r, body, authHeader)
+}
+
+// verifyProxyRequest mirrors server-demo/handler.go steps 0-4: protocol
+// version, body SHA256, target validation, and HMAC signature verification.
+// It records whether verification ran and its result (for assertions) and
+// returns the auth header the client committed to. On any failure it writes
+// the HTTP error and returns ok=false.
+func (s *inTestSidecar) verifyProxyRequest(w http.ResponseWriter, r *http.Request, body []byte) (authHeader string, ok bool) {
+	// Step 0: protocol version.
+	version := r.Header.Get(sidecar.HeaderProxyVersion)
+	if version != sidecar.ProtocolV1 {
+		http.Error(w, "unsupported "+sidecar.HeaderProxyVersion+": "+version, http.StatusBadRequest)
+		return "", false
+	}
+
+	// Step 1-2: timestamp + body SHA256.
+	ts := r.Header.Get(sidecar.HeaderProxyTimestamp)
+	claimedSHA := r.Header.Get(sidecar.HeaderBodySHA256)
+	if claimedSHA == "" || claimedSHA != sidecar.BodySHA256(body) {
+		http.Error(w, "body SHA256 mismatch", http.StatusBadRequest)
+		return "", false
+	}
+
+	// Step 3: target host, identity, auth-header (all covered by the sig).
+	targetHost, perr := parseTargetHost(r.Header.Get(sidecar.HeaderProxyTarget))
+	if perr != nil {
+		http.Error(w, "invalid "+sidecar.HeaderProxyTarget+": "+perr.Error(), http.StatusForbidden)
+		return "", false
+	}
+	identity := r.Header.Get(sidecar.HeaderProxyIdentity)
+	authHeader = r.Header.Get(sidecar.HeaderProxyAuthHeader)
+
+	// Step 4: verify HMAC signature over the canonical request.
+	err := sidecar.Verify(s.key, sidecar.CanonicalRequest{
+		Version:      version,
+		Method:       r.Method,
+		Host:         targetHost,
+		PathAndQuery: r.URL.RequestURI(),
+		BodySHA256:   claimedSHA,
+		Timestamp:    ts,
+		Identity:     identity,
+		AuthHeader:   authHeader,
+	}, r.Header.Get(sidecar.HeaderProxySignature))
+	s.mu.Lock()
+	s.verifyRan = true
+	s.verifyErr = err
+	s.mu.Unlock()
+	if err != nil {
+		http.Error(w, "HMAC verification failed: "+err.Error(), http.StatusUnauthorized)
+		return "", false
+	}
+	return authHeader, true
+}
+
+// forwardWithInjectedToken mirrors server-demo's inject+forward. Unlike
+// server-demo (which forwards to "https://"+targetHost), this test forwards to
+// the in-test MOCK's URL — proving the sidecar's inject step without needing a
+// real upstream or a route to targetHost. It strips any client-supplied auth
+// headers first (the sidecar is the sole source of auth material), injects the
+// synthetic token into the committed header, and relays the response back.
+func (s *inTestSidecar) forwardWithInjectedToken(w http.ResponseWriter, r *http.Request, body []byte, authHeader string) {
+	freq, err := http.NewRequest(r.Method, s.upstreamURL+r.URL.RequestURI(), bytes.NewReader(body))
+	if err != nil {
+		http.Error(w, "failed to build forward request", http.StatusInternalServerError)
+		return
+	}
+	for k, vs := range r.Header {
+		if isProxyHeader(k) {
+			continue
+		}
+		for _, v := range vs {
+			freq.Header.Add(k, v)
+		}
+	}
+	freq.Header.Del("Authorization")
+	freq.Header.Del(sidecar.HeaderMCPUAT)
+	freq.Header.Del(sidecar.HeaderMCPTAT)
+
+	if authHeader == "Authorization" {
+		freq.Header.Set("Authorization", "Bearer "+injectedToken)
+	} else {
+		freq.Header.Set(authHeader, injectedToken)
+	}
+
+	resp, err := http.DefaultClient.Do(freq)
+	if err != nil {
+		http.Error(w, "forward failed: "+err.Error(), http.StatusBadGateway)
+		return
+	}
+	defer resp.Body.Close()
+	respBody, _ := io.ReadAll(resp.Body)
+	for k, vs := range resp.Header {
+		for _, v := range vs {
+			w.Header().Add(k, v)
+		}
+	}
+	w.WriteHeader(resp.StatusCode)
+	_, _ = w.Write(respBody)
+}
+
+// verifyResult reports whether step 4 ran and, if so, its error.
+func (s *inTestSidecar) verifyResult() (ran bool, err error) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	return s.verifyRan, s.verifyErr
+}
+
+// isProxyHeader reports whether name is one of the sidecar wire-protocol
+// headers that must not be copied through to the forwarded (mock upstream)
+// request. Mirrors sidecar/server-demo/handler.go's isProxyHeader.
+func isProxyHeader(name string) bool {
+	switch http.CanonicalHeaderKey(name) {
+	case http.CanonicalHeaderKey(sidecar.HeaderProxyVersion),
+		http.CanonicalHeaderKey(sidecar.HeaderProxyTarget),
+		http.CanonicalHeaderKey(sidecar.HeaderProxyIdentity),
+		http.CanonicalHeaderKey(sidecar.HeaderProxySignature),
+		http.CanonicalHeaderKey(sidecar.HeaderProxyTimestamp),
+		http.CanonicalHeaderKey(sidecar.HeaderBodySHA256),
+		http.CanonicalHeaderKey(sidecar.HeaderProxyAuthHeader):
+		return true
+	}
+	return false
+}
+
+// parseTargetHost validates X-Lark-Proxy-Target and returns its host.
+// Mirrors sidecar/server-demo/handler.go's parseTarget: the header must be
+// "https://<host>" with no path, query, fragment, or userinfo. Only the host
+// is used, both as HMAC signing input and to record what the fork believed
+// its real destination was — the actual forward in this test always goes to
+// the in-test mock, never to this host.
+func parseTargetHost(target string) (string, error) {
+	u, err := url.Parse(target)
+	if err != nil {
+		return "", fmt.Errorf("parse: %w", err)
+	}
+	if u.Scheme != "https" {
+		return "", fmt.Errorf("scheme must be https, got %q", u.Scheme)
+	}
+	if u.Host == "" {
+		return "", fmt.Errorf("missing host")
+	}
+	if u.User != nil {
+		return "", fmt.Errorf("userinfo not allowed")
+	}
+	if u.Path != "" && u.Path != "/" {
+		return "", fmt.Errorf("path not allowed (got %q)", u.Path)
+	}
+	if u.RawQuery != "" {
+		return "", fmt.Errorf("query not allowed")
+	}
+	if u.Fragment != "" {
+		return "", fmt.Errorf("fragment not allowed")
+	}
+	return u.Host, nil
+}
+
+// --- fork build + run ------------------------------------------------------
+
+// buildAuthsidecarFork builds the REAL lark-cli with -tags authsidecar (the
+// production interceptor) and returns the binary path.
+func buildAuthsidecarFork(t *testing.T) string {
+	t.Helper()
+	bin := filepath.Join(t.TempDir(), "forkbin")
+	build := exec.Command("go", "build", "-tags", "authsidecar", "-o", bin, ".")
+	build.Dir = repoRoot(t)
+	if out, err := build.CombinedOutput(); err != nil {
+		t.Fatalf("build fork binary: %v\n%s", err, out)
+	}
+	return bin
+}
+
+// runFork runs the fork against the in-test sidecar, fully offline. The fork's
+// exit status is logged but NOT asserted — this test judges wire behavior
+// (what reached the sidecar/upstream), not the command's own success.
+func runFork(t *testing.T, binPath, sidecarURL string) {
+	t.Helper()
+	scURL, err := url.Parse(sidecarURL)
+	if err != nil {
+		t.Fatalf("parse sidecar URL: %v", err)
+	}
+
+	ctx, cancel := context.WithTimeout(context.Background(), 60*time.Second)
+	defer cancel()
+	cmd := exec.CommandContext(ctx, binPath, "docs", "+fetch", "--doc", "nonexistent", "--as", "user")
+	cmd.Env = append(os.Environ(),
+		"LARKSUITE_CLI_AUTH_PROXY=http://"+scURL.Host,
+		"LARKSUITE_CLI_PROXY_KEY="+testProxyKey,
+		"LARKSUITE_CLI_APP_ID="+testAppID,
+		"LARKSUITE_CLI_BRAND=feishu",
+		"LARKSUITE_CLI_CONFIG_DIR="+t.TempDir(),
+		"LARKSUITE_CLI_NO_UPDATE_NOTIFIER=1",
+		"LARKSUITE_CLI_NO_SKILLS_NOTIFIER=1",
+	)
+	var stdout, stderr bytes.Buffer
+	cmd.Stdout = &stdout
+	cmd.Stderr = &stderr
+	runErr := cmd.Run()
+	t.Logf("fork exit error (informational only, not asserted): %v", runErr)
+	t.Logf("fork stdout: %s", stdout.String())
+	t.Logf("fork stderr: %s", stderr.String())
+}
+
+// repoRoot resolves the lark-cli module root from the test's working
+// directory (which `go test` sets to the package dir, tests/sidecar_e2e).
+func repoRoot(t *testing.T) string {
+	t.Helper()
+	out, err := exec.Command("git", "rev-parse", "--show-toplevel").Output()
+	if err != nil {
+		t.Fatalf("resolve repo root: %v", err)
+	}
+	return strings.TrimSpace(string(out))
+}
+
+// --- assertions ------------------------------------------------------------
+
+// assertInterceptorSigned checks the fork -> sidecar hop (assertions a + c):
+// the real interceptor ran (all proxy headers present, identity=user), stripped
+// every real/sentinel auth header before signing, and produced a signature that
+// verified against the shared key.
+func assertInterceptorSigned(t *testing.T, sc *inTestSidecar) {
+	t.Helper()
+	got := sc.sink.get()
+	if got == nil {
+		t.Fatal("sidecar never received a request from the fork — interceptor did not route to AUTH_PROXY")
+	}
+	ran, verifyErr := sc.verifyResult()
+	if !ran {
+		t.Fatal("sidecar received a request but never reached HMAC verification (rejected earlier — see handler headers)")
+	}
+	if verifyErr != nil {
+		t.Fatalf("HMAC verification failed on the fork's own signed request: %v", verifyErr)
+	}
+	t.Logf("fork->sidecar headers: %v", got.headers)
+
+	// No real/sentinel auth ever left the fork: the interceptor strips the
+	// sentinel before signing, so this hop must carry no auth header at all.
+	if auth := got.headers.Get("Authorization"); auth != "" {
+		t.Fatalf("fork->sidecar hop leaked an Authorization header (want none, interceptor should have stripped it): %q", auth)
+	}
+	if v := got.headers.Get(sidecar.HeaderMCPUAT); v != "" {
+		t.Fatalf("fork->sidecar hop leaked %s (want none): %q", sidecar.HeaderMCPUAT, v)
+	}
+	if v := got.headers.Get(sidecar.HeaderMCPTAT); v != "" {
+		t.Fatalf("fork->sidecar hop leaked %s (want none): %q", sidecar.HeaderMCPTAT, v)
+	}
+
+	// Proxy headers must be present (proves the interceptor actually ran).
+	for _, h := range []string{
+		sidecar.HeaderProxyVersion, sidecar.HeaderProxyTarget, sidecar.HeaderProxyIdentity,
+		sidecar.HeaderProxySignature, sidecar.HeaderProxyTimestamp, sidecar.HeaderBodySHA256,
+		sidecar.HeaderProxyAuthHeader,
+	} {
+		if got.headers.Get(h) == "" {
+			t.Fatalf("fork->sidecar hop missing required proxy header %s", h)
+		}
+	}
+	if id := got.headers.Get(sidecar.HeaderProxyIdentity); id != sidecar.IdentityUser {
+		t.Fatalf("fork->sidecar identity = %q, want %q", id, sidecar.IdentityUser)
+	}
+}
+
+// assertInjectedTokenReachedUpstream checks the sidecar -> upstream hop
+// (assertion b): the mock saw exactly the sidecar-injected synthetic token,
+// never a sentinel or a real one — proving injection actually happened.
+func assertInjectedTokenReachedUpstream(t *testing.T, up *mockUpstream) {
+	t.Helper()
+	got := up.sink.get()
+	if got == nil {
+		t.Fatal("mock upstream never received a forwarded request — sidecar did not forward after verification")
+	}
+	t.Logf("sidecar->mock headers: %v", got.headers)
+
+	wantAuth := "Bearer " + injectedToken
+	gotAuth := got.headers.Get("Authorization")
+	if gotAuth != wantAuth {
+		t.Fatalf("mock upstream Authorization = %q, want %q", gotAuth, wantAuth)
+	}
+	// Belt-and-suspenders: the value the mock saw must not be either sentinel,
+	// proving the only token that ever reached "upstream" was the injected one.
+	if gotAuth == "Bearer "+sidecar.SentinelUAT || gotAuth == "Bearer "+sidecar.SentinelTAT {
+		t.Fatalf("mock upstream received a sentinel token instead of the injected one: %q", gotAuth)
+	}
+}