feat: launcher override chain for Claude plugins

[umputun]

Adds a two-layer override chain (user → bundled) for the launcher scripts shipped by both Claude plugins, so users can drop a custom launcher at ${CLAUDE_PLUGIN_DATA}/scripts/<launcher>.sh without forking the plugin.

Resolves the action item from discussion #121.

What's new

• .claude-plugin/skills/revdiff/scripts/resolve-launcher.sh — walks the override chain, returns the path of the first executable launcher
• plugins/revdiff-planning/scripts/resolve-launcher.sh — same shape for the plan-review hook
• plan-review-hook.py resolves the launcher through the same chain (with cwd=CLAUDE_PROJECT_DIR pinning for hygiene)
• Plugin versions: revdiff 0.7.6 → 0.8.0, revdiff-planning 0.2.2 → 0.3.0 (also resyncs the marketplace.json drift on revdiff-planning)
• Doc updates across README.md, CLAUDE.md, site/docs.html, install.md, the new plugins/revdiff-planning/README.md, and a Claude-only note in plugins/codex/skills/revdiff/SKILL.md

Why no project layer

The original plan included a third .claude/<plugin-namespace>/scripts/ project layer matching cc-thingz. Codex external review flagged it as a security risk: the revdiff-planning hook fires automatically on every ExitPlanMode in any repo Claude opens, so a repo-controlled executable at that path would auto-execute on routine actions without per-repo opt-in. Project layer was dropped from both resolvers (commit 5e58e8c); diff-review skill keeps the same shape for symmetry. cc-thingz's project layer is fine because it resolves prompt files (read by Claude, not executed) — different threat model.

Notable hardening from the review loop

• from __future__ import annotations so the hook stays Python 3.9 compatible (macOS system Python). PEP 604 Path | None would otherwise crash at module load.
• [ -f path ] && [ -x path ] in both resolvers so a directory at the override path doesn't win over the bundled launcher.
• Quoted ${CLAUDE_PLUGIN_DATA} and ${CLAUDE_SKILL_DIR} in the resolver invocation so paths with spaces work.
• Quoted ${CLAUDE_PLUGIN_ROOT} in hooks.json (pre-existing bug, fixed per the no-pre-existing-issues policy).
• __pycache__/ and *.pyc added to .gitignore.

Backward compatibility

Zero behavior change for users with no overrides — bundled launcher is still the default.

Out of scope (already covered in CLAUDE.md / docs)

• Codex skills: user owns ~/.codex/skills/ and edits launchers directly there
• OpenCode setup: copies launchers to ~/.config/opencode/, user-owned
• Pi extension: no CLAUDE_PLUGIN_DATA in Pi runtime; documented asymmetry

[Copilot]

Pull request overview

Adds a consistent “user → bundled” launcher-override mechanism for the two Claude plugins (diff-review skill + plan-review hook), allowing per-user launcher customization via ${CLAUDE_PLUGIN_DATA} without forking, with docs updated to reflect the security-driven omission of any project-level override.

Changes:

• Added resolve-launcher.sh resolvers (one per plugin) to select the first executable launcher from user → bundled.
• Updated revdiff-planning hook to resolve launch-plan-review.sh via the resolver (and pinned resolver cwd to CLAUDE_PROJECT_DIR).
• Bumped plugin versions and updated docs across README/CLAUDE/site docs and plugin-specific references.

Reviewed changes

Copilot reviewed 15 out of 16 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
site/docs.html	Documents the new override chain and clarifies pi/Codex asymmetry.
plugins/revdiff-planning/scripts/resolve-launcher.sh	New resolver script for plan-review launcher (user → bundled).
plugins/revdiff-planning/scripts/plan-review-hook.py	Uses resolver to locate launcher before invoking revdiff overlay.
plugins/revdiff-planning/hooks/hooks.json	Quotes ${CLAUDE_PLUGIN_ROOT} path in the hook command.
plugins/revdiff-planning/README.md	New plugin README including override instructions and rationale.
plugins/revdiff-planning/.claude-plugin/plugin.json	Version bump for revdiff-planning.
plugins/codex/skills/revdiff/SKILL.md	Notes that Claude-style overrides don’t apply to Codex skills.
docs/plans/completed/20260419-launcher-override-chain.md	Archived plan documenting final (post-security-review) two-layer design.
README.md	Adds “Custom launchers” section + pi runtime clarification.
CLAUDE.md	Documents override chain + local testing commands.
.gitignore	Ignores Python bytecode artifacts.
.claude-plugin/skills/revdiff/scripts/resolve-launcher.sh	New resolver script for diff-review launcher (user → bundled).
.claude-plugin/skills/revdiff/references/install.md	Documents override paths + guidance for safe launcher customization.
.claude-plugin/skills/revdiff/SKILL.md	Switches launcher invocation to resolver-based command substitution.
.claude-plugin/plugin.json	Version bump for revdiff Claude plugin.
.claude-plugin/marketplace.json	Updates marketplace versions (and syncs planning drift).

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[umputun]

This finding is incorrect — from __future__ import annotations (PEP 563) does make Path | None work on Python 3.9.

Mechanism: PEP 563 (available since 3.7) stores all annotations as string literals at compile time and never evaluates them. Path | None is syntactically valid Python regardless of version (| is a normal expression operator), and with the future import the runtime semantic of type | type is never invoked. PEP 604 (3.10+) only adds the runtime meaning — the string is just a string until something explicitly calls typing.get_type_hints(), which this hook does not.

Verified empirically on macOS system Python 3.9.6:

$ /usr/bin/python3 --version
Python 3.9.6

$ /usr/bin/python3 -c "
import importlib.util
spec = importlib.util.spec_from_file_location('h', 'plugins/revdiff-planning/scripts/plan-review-hook.py')
m = importlib.util.module_from_spec(spec)
spec.loader.exec_module(m)
print('annotation type:', type(m.resolve_launcher.__annotations__['return']).__name__)
print('annotation value:', repr(m.resolve_launcher.__annotations__['return']))
"
annotation type: str
annotation value: 'Path | None'

Module imports clean, no SyntaxError, annotation lives as the string 'Path | None' exactly per PEP 563.

Keeping the current code.