feat(devin): add SessionEnd hook for activity tracking (#5)

The Claude Code plugin ships a SessionEnd hook that logs a cheap timestamp
+ PWD marker to ~/.skillopt-sleep/session-end.log so the next nightly cycle
knows there is fresh activity to harvest. The Devin plugin had no
equivalent — nightly runs relied on cron alone with no activity signal.

Devin CLI supports SessionEnd hooks via .devin/hooks.v1.json (same JSON
format as Claude Code), firing with {"reason": "..."} on stdin and setting
DEVIN_PROJECT_DIR to the project root.

Add hooks/hooks.v1.json (SessionEnd hook config) and
hooks/on-session-end.sh (mirrors the Claude Code on-session-end.sh: append
timestamp + project dir, non-blocking, no API spend). Update README install
instructions with the optional copy step.

plugins/devin/README.md

@@ -16,7 +16,10 @@ source into the Claude Code-compatible JSONL the engine reads.
 | `harvest_devin.py` | converts Devin ATIF-v1.7 transcripts + agentmemory + `.devin/skills` into JSONL, with `taskKey` + outcome envelopes |
 | `judge.py` | reference judge for the deferred/judge branch of the validation gate |
 | `mcp-config.example.json` | drop-in MCP server config |
-| `devin-rules.snippet.md` | paste into `.devin/rules/skillopt-sleep.md` |
+| `install.sh` | copies hooks + rules into a project's `.devin/` and prints the MCP registration command |
+| `devin-rules.snippet.md` | copied to `.devin/rules/skillopt-sleep.md` by `install.sh` |
+| `hooks/hooks.v1.json` | SessionEnd hook config — copied to `.devin/hooks.v1.json` by `install.sh` |
+| `hooks/on-session-end.sh` | best-effort activity marker script (called by the hook) |
 
 ## What it harvests
 
@@ -33,10 +36,20 @@ After `sleep_adopt`, the evolved skill is synced to `.devin/skills/skillopt-slee
 
 Requires Python ≥ 3.10. No third-party packages — the server is pure stdlib.
 
-1. **Register the MCP server.** Use `mcp-config.example.json` as a template; set
-   `args` to the absolute path of this `mcp_server.py`. The engine is found
-   automatically (this plugin lives inside the SkillOpt repo). Or via the Devin
-   CLI:
+1. **Install hooks + rules into your project.** From the repo root:
+
+   ```bash
+   bash plugins/devin/install.sh /path/to/your/project
+   ```
+
+   This copies the SessionEnd hook and rules snippet into the project's
+   `.devin/` directory and prints the MCP registration command. The hook is
+   on by default — it logs a cheap activity marker when each session ends so
+   the next nightly cycle knows there is fresh data to harvest. It is
+   non-blocking and spends no API budget. Re-run the script to update.
+
+2. **Register the MCP server.** Use `mcp-config.example.json` as a template, or
+   run the command printed by `install.sh`:
 
    ```bash
    devin mcp add skillopt-sleep \
@@ -44,9 +57,6 @@ Requires Python ≥ 3.10. No third-party packages — the server is pure stdlib.
      -- python3 /abs/path/to/SkillOpt/plugins/devin/mcp_server.py
    ```
 
-2. **(Optional)** copy `devin-rules.snippet.md` to `.devin/rules/skillopt-sleep.md`
-   so Devin proactively offers the tools.
-
 3. Ask Devin: *"run the sleep cycle"*, *"what did the last sleep propose?"*, *"adopt it"*.
 
 ## Tools

plugins/devin/hooks/hooks.v1.json

@@ -0,0 +1,14 @@
+{
+  "SessionEnd": [
+    {
+      "matcher": "",
+      "hooks": [
+        {
+          "type": "command",
+          "command": "\"${DEVIN_PROJECT_DIR}/.devin/hooks/on-session-end.sh\"",
+          "timeout": 5
+        }
+      ]
+    }
+  ]
+}

plugins/devin/hooks/on-session-end.sh

@@ -0,0 +1,20 @@
+#!/usr/bin/env bash
+# SkillOpt-Sleep SessionEnd hook for Devin (best-effort, NON-BLOCKING).
+#
+# This does NOT run the optimizer. It only appends a tiny marker so the next
+# nightly cycle knows there is fresh activity to harvest, and (optionally)
+# nudges the user once that a sleep cycle is available. It must never fail the
+# session or spend API budget.
+#
+# Install: copy this file and hooks.v1.json into your project's .devin/hooks/
+# directory. Devin CLI reads .devin/hooks.v1.json automatically.
+set -uo pipefail
+
+STATE_DIR="${HOME}/.skillopt-sleep"
+mkdir -p "$STATE_DIR" 2>/dev/null || exit 0
+
+# Record that a session just ended (cheap; used for "is there new data?").
+printf '%s\t%s\n' "$(date -u +%Y-%m-%dT%H:%M:%SZ)" "${DEVIN_PROJECT_DIR:-${PWD}}" \
+  >> "$STATE_DIR/session-end.log" 2>/dev/null || true
+
+exit 0

plugins/devin/install.sh

@@ -0,0 +1,59 @@
+#!/usr/bin/env bash
+# Install the SkillOpt-Sleep Devin integration into a project.
+# Copies the SessionEnd hook and rules snippet into .devin/, and prints
+# the MCP server registration command. Idempotent.
+set -euo pipefail
+
+PLUGIN_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+REPO_ROOT="$(cd "$PLUGIN_DIR/../.." && pwd)"
+PROJECT="${1:-$(pwd)}"
+
+echo "[install] repo: $REPO_ROOT"
+echo "[install] project: $PROJECT"
+
+DEVIN_DIR="$PROJECT/.devin"
+mkdir -p "$DEVIN_DIR/hooks" "$DEVIN_DIR/rules"
+
+# 1) SessionEnd hook (on by default — provides activity signal for nightly harvest)
+#    Merge into existing hooks.v1.json instead of overwriting, so we don't
+#    destroy other project hooks.
+HOOK_SCRIPT_SRC="$PLUGIN_DIR/hooks/on-session-end.sh"
+HOOK_SCRIPT_DST="$DEVIN_DIR/hooks/on-session-end.sh"
+cp "$HOOK_SCRIPT_SRC" "$HOOK_SCRIPT_DST"
+chmod +x "$HOOK_SCRIPT_DST"
+echo "[install] hook script       -> $HOOK_SCRIPT_DST"
+
+HOOK_CONFIG="$DEVIN_DIR/hooks.v1.json"
+if [ -f "$HOOK_CONFIG" ]; then
+  # Merge our SessionEnd hook into the existing config (jq deep-merge)
+  if command -v jq >/dev/null 2>&1; then
+    jq -s '.[0] * .[1]' "$HOOK_CONFIG" "$PLUGIN_DIR/hooks/hooks.v1.json" > "$HOOK_CONFIG.tmp"
+    mv "$HOOK_CONFIG.tmp" "$HOOK_CONFIG"
+    echo "[install] session-end hook  -> $HOOK_CONFIG (merged)"
+  else
+    echo "[install] WARNING: jq not found; cannot merge into existing $HOOK_CONFIG"
+    echo "[install] Merge this SessionEnd hook manually or install jq:"
+    echo "[install]   cat $PLUGIN_DIR/hooks/hooks.v1.json"
+    echo "[install] Skipping hook config to avoid overwriting existing hooks."
+  fi
+else
+  cp "$PLUGIN_DIR/hooks/hooks.v1.json" "$HOOK_CONFIG"
+  echo "[install] session-end hook  -> $HOOK_CONFIG"
+fi
+
+# 2) Rules snippet so Devin proactively offers the tools
+cp "$PLUGIN_DIR/devin-rules.snippet.md" "$DEVIN_DIR/rules/skillopt-sleep.md"
+echo "[install] rules snippet     -> $DEVIN_DIR/rules/skillopt-sleep.md"
+
+# 3) Print the MCP server registration command
+cat <<EOF
+
+[install] Register the MCP server (run once per machine):
+
+  devin mcp add skillopt-sleep \\
+    --env "SKILLOPT_DEVIN_CLAUDE_HOME=\$HOME/.skillopt-sleep-devin" \\
+    -- python3 $PLUGIN_DIR/mcp_server.py
+
+Done. Try asking Devin:
+  Run the sleep cycle for this project.
+EOF