Document the repo tool execution contract (docs audit)

[selfcontained]

Nightly docs audit — Repo Tools deep-dive (the next_focus carried over three runs), checked against apps/server/src/shared/mcp/repo-tools.ts, shared/mcp/server.ts, agents/lifecycle-hooks.ts and shared/lib/run-command.ts.

Verified clean: the docs-pane built-in tools list matches AGENT_TOOLS as a set in both directions (63 entries), the repo_ prefixing and dot-sanitization claim, the "runs at the root of the agent's checkout" claim (toolsRoot = worktreeRoot ?? repoRoot), the agent/job scope pair (reviewer remains reachable in VALID_SCOPES but is never set — deliberately undocumented), and the hooks' 15s / best-effort claims.

Fixed — docs-pane tools.tsx:

• Commands are spawned directly, not through a shell, so pipes/globs/&& don't work.
• name, description and a non-empty command array are required, and one malformed entry throws during the manifest load, which surfaces as every repo_ tool disappearing rather than as a parse error.
• New "What agents get back": repo tools allow every exit code (allowedExitCodes 0–255), so stdout is the text result with exit code/stdout/stderr alongside — a non-zero exit is something the agent reads, not an error. Dispatch imposes no timeout on them, unlike hooks.
• New "Picking up changes": the manifest is re-read per tool listing (only hooks are mtime-cached), but a CLI holds the tool list it fetched at session start — so an edited command runs the new version on the next call while a newly added tool needs a new session.
• Params: empty-string values are skipped too; name/type/flag required, description is what the agent reads.

Fixed — plugins/dispatch/skills/repo-tools/SKILL.md: the claim that a name colliding with a built-in is "rejected at load" is false — BUILTIN_TOOL_NAMES holds unprefixed names while the check tests the repo_-prefixed one, so it can never fire. Reworded to say the prefix is what prevents collisions. Also tightened "run from the repo root" to the agent's checkout root, and noted the no-shell spawn and the hook's 15s timeout.

Tip (Phase 2b): added an ambient repo-tools tip. .dispatch/tools.json has no UI surface whatsoever and had no tip, which is exactly the discovery gap tips exist for. Links to the Repo Tools docs section.

CLAUDE.md: project tree gains plugins/ (new in #952) and release-notes/ (referenced by a whole section but absent from the tree).

Deferred to next run: the Dispatch plugin (#952) has README coverage but zero in-app docs — a docs-pane section plus a matching install tip is the next focus. Also backlogged: the dead BUILTIN_TOOL_NAMES collision check, and the dead exitCode !== 0 warn branch in lifecycle-hooks.ts (runCommand defaults to allowedExitCodes: [0], so a failing hook rejects before that branch is reached — the documented behavior is unaffected).

Verified: pnpm run format:write, pnpm run check, apps/web tips tests, apps/server plugin-manifest tests.