feat: Git extension stage 2 — GIT_BRANCH_NAME override, --force for existing dirs, auto-install tests (#1940) (#2117)

* feat: Git extension stage 2 — GIT_BRANCH_NAME override, --force for existing dirs, auto-install tests (#1940)

- Add GIT_BRANCH_NAME env var override to create-new-feature.sh/.ps1
  for exact branch naming (bypasses all prefix/suffix generation)
- Fix --force flag for 'specify init <dir>' into existing directories
- Add TestGitExtensionAutoInstall tests (auto-install, --no-git skip,
  commands registered)
- Add TestFeatureDirectoryResolution tests (env var, feature.json,
  priority, branch fallback)
- Document GIT_BRANCH_NAME in speckit.git.feature.md and specify.md

* fix: remove unused Tuple import (ruff F401)

* fix: address Copilot review feedback (#2117)

- Fix timestamp regex ordering: check YYYYMMDD-HHMMSS before generic
  numeric prefix in both bash and PowerShell
- Set BRANCH_SUFFIX in GIT_BRANCH_NAME override path so 244-byte
  truncation logic works correctly
- Add 244-byte length check for GIT_BRANCH_NAME in PowerShell
- Use existing_items for non-empty dir warning with --force
- Skip git extension install if already installed (idempotent --force)
- Wrap PowerShell feature.json parsing in try/catch for malformed JSON
- Fix PS comment: 'prefix lookup' -> 'exact mapping via Get-FeatureDir'
- Remove non-functional SPECIFY_SPEC_DIRECTORY from specify.md template

* fix: address second round of Copilot review feedback (#2117)

- Guard shutil.rmtree on init failure: skip cleanup when --force merged
  into a pre-existing directory (prevents data loss)
- Bash: error on GIT_BRANCH_NAME >244 bytes instead of broken truncation
- Fix malformed numbered list in specify.md (restore missing step 1)
- Add claude_skills.exists() assert before iterdir() in test

* fix: use UTF-8 byte count for 244-byte branch name limit (#2117)

- Bash: use LC_ALL=C wc -c for byte length instead of ${#VAR}
- PowerShell: use [System.Text.Encoding]::UTF8.GetByteCount() instead
  of .Length (UTF-16 code units)

* fix: address third round of review feedback (#2117)

- Update --dry-run help text in bash and PowerShell (branch name only)
- Fix specify.md JSON example: use concrete path, not literal variable
- Add TestForceExistingDirectory tests (merge + error without --force)
- Add PowerShell Get-FeaturePathsEnv tests (env var + feature.json)

* fix: normalize relative paths and fix Test-HasGit compat (#2117)

- Bash common.sh: normalize SPECIFY_FEATURE_DIRECTORY and feature.json
  relative paths to absolute under repo root
- PowerShell common.ps1: same normalization using IsPathRooted + Join-Path
- PowerShell create-new-feature.ps1: call Test-HasGit without -RepoRoot
  for compatibility with core common.ps1 (no param) and git-common.ps1
  (optional param with default)

* test: add GIT_BRANCH_NAME automated tests for bash and PowerShell (#2117)

- TestGitBranchNameOverrideBash: 5 tests (exact name, sequential prefix,
  timestamp prefix, overlong rejection, dry-run)
- TestGitBranchNameOverridePowerShell: 4 tests (exact name, sequential
  prefix, timestamp prefix, overlong rejection)
- Tests use extension scripts (not core) via new ext_git_repo and
  ext_ps_git_repo fixtures

* fix: restore git init during specify init + review fixes (#2117)

- Restore is_git_repo() and init_git_repo() functions removed in stage 2
- specify init now runs git init AND installs git extension (not just
  extension install alone)
- Add is_dir() guard for non-here path to prevent uncontrolled error
  when target exists but is a file
- Add python3 JSON fallback in common.sh for multi-line feature.json
  (grep pipeline fails on pretty-printed JSON without jq)

* fix: use init_git_repo error_msg in failure output (#2117)

* fix: ensure_executable_scripts also covers .specify/extensions/ (#2117)

Extension .sh scripts (e.g. create-new-feature.sh, initialize-repo.sh)
may lack execute bits after install. Scan both .specify/scripts/ and
.specify/extensions/ for permission fixing.

* fix: move chmod after extension install + sanitize error_msg (#2117)

- ensure_executable_scripts() now runs after git extension install so
  extension .sh files get execute bits in the same init run
- Sanitize init_git_repo error_msg to single line (replace newlines,
  truncate to 120 chars) to prevent garbled StepTracker output

* fix: use tracker.error for git init/extension failures (#2117)

Git init failure and extension install failure were reported as
tracker.complete (showing green) even on error. Now track a
git_has_error flag and call tracker.error when any step fails,
so the UI correctly reflects the failure state.

* fix: sanitize ext_err in git step tracker for consistent rendering (#2117)

extensions/git/commands/speckit.git.feature.md

@@ -4,7 +4,7 @@ description: "Create a feature branch with sequential or timestamp numbering"
 
 # Create Feature Branch
 
-Create a new feature branch for the given specification.
+Create and switch to a new git feature branch for the given specification. This command handles **branch creation only** — the spec directory and files are created by the core `/speckit.specify` workflow.
 
 ## User Input
 
@@ -14,10 +14,17 @@ $ARGUMENTS
 
 You **MUST** consider the user input before proceeding (if not empty).
 
+## Environment Variable Override
+
+If the user explicitly provided `GIT_BRANCH_NAME` (e.g., via environment variable, argument, or in their request), pass it through to the script by setting the `GIT_BRANCH_NAME` environment variable before invoking the script. When `GIT_BRANCH_NAME` is set:
+- The script uses the exact value as the branch name, bypassing all prefix/suffix generation
+- `--short-name`, `--number`, and `--timestamp` flags are ignored
+- `FEATURE_NUM` is extracted from the name if it starts with a numeric prefix, otherwise set to the full branch name
+
 ## Prerequisites
 
 - Verify Git is available by running `git rev-parse --is-inside-work-tree 2>/dev/null`
-- If Git is not available, warn the user and skip branch creation (spec directory will still be created)
+- If Git is not available, warn the user and skip branch creation
 
 ## Branch Numbering Mode
 
@@ -45,22 +52,16 @@ Run the appropriate script based on your platform:
 - Do NOT pass `--number` — the script determines the correct next number automatically
 - Always include the JSON flag (`--json` for Bash, `-Json` for PowerShell) so the output can be parsed reliably
 - You must only ever run this script once per feature
-- The JSON output will contain BRANCH_NAME and SPEC_FILE paths
-
-If the extension scripts are not found at the `.specify/extensions/git/` path, fall back to:
-- **Bash**: `scripts/bash/create-new-feature.sh`
-- **PowerShell**: `scripts/powershell/create-new-feature.ps1`
+- The JSON output will contain `BRANCH_NAME` and `FEATURE_NUM`
 
 ## Graceful Degradation
 
 If Git is not installed or the current directory is not a Git repository:
-- The script will still create the spec directory under `specs/`
-- A warning will be printed: `[specify] Warning: Git repository not detected; skipped branch creation`
-- The workflow continues normally without branch creation
+- Branch creation is skipped with a warning: `[specify] Warning: Git repository not detected; skipped branch creation`
+- The script still outputs `BRANCH_NAME` and `FEATURE_NUM` so the caller can reference them
 
 ## Output
 
 The script outputs JSON with:
-- `BRANCH_NAME`: The created branch name (e.g., `003-user-auth` or `20260319-143022-user-auth`)
-- `SPEC_FILE`: Path to the created spec file
+- `BRANCH_NAME`: The branch name (e.g., `003-user-auth` or `20260319-143022-user-auth`)
 - `FEATURE_NUM`: The numeric or timestamp prefix used