feat: stateless phase gate and gated tools

[renezander030]

What changed

• phase gate. Ordered phases, each with requires (ids of other gates). Being in a phase requires the gates of that phase and every earlier one to pass when checked. The active phase is read from a plain marker file (.skillgate/phase by default). Nothing is stored or signed, and each required gate runs once per run.
• skillgate phase [<id>]. Without an id it shows each phase's status. With an id it moves to that phase only if the phase's requirements pass (exit 2 otherwise).
• gatedTools. Tool-name globs that cross the finish line like finishLine commands, for example MCP tools that publish or deploy. Where it is checked:
  • skillgate gate reads the tool name from the Claude Code, Codex and Gemini CLI hook payload, or takes --tool <name>.
  • The opencode plugin checks it in tool.execute.before.
  • install adds the tools to the hook matcher, and doctor flags a hook whose matcher does not cover them.
• when.tool. Scopes a gate to gated tools, alongside when.command.

Why

Closes #18. This is the reduced design agreed in that thread: a stateless phase gate evaluated live, plus tool gating. There is no salt and no hash chain. A phase marker can't be forged into passing, because every check re-runs the requirements against the workspace. Thanks @watanabefam for the proposal.

How I verified it

npm run build && npm run test:coverage   # Node 22: 163 pass, 0 fail; lines 93.5%, branches 80.9%, functions 97.6%
node dist/src/cli.js check                # dogfood policy passes

• 12 new tests in test/phase.test.ts:
  • phase gate: cumulative live requirements, marker handling, run-once memo, validation
  • skillgate phase: moving between phases and the status output
  • gated tools: decideTool and when.tool, hook payloads (Claude, Gemini format, --tool)
  • opencode plugin: gated tools and the invalid-policy behaviour
  • install matchers and the doctor coverage check
• Live smoke test: with gatedTools: ['Write'] and the matcher written by install claude-code (Bash|Write), a real Claude Code session's Write call was blocked with the unmet gate, and the file was never created.

Review notes

• Base: master at 0.10.1.
• Behaviour change: in the opencode plugin, an invalid policy still blocks shell commands but no longer blocks other tools, so the agent can edit the policy to fix it. Before this, non-bash tools skipped the policy entirely.
• Cursor's hook covers shell commands only, so gatedTools does not apply there. The docs say so.
• Changes are under ## Unreleased. Tag v0.11.0 after merge.

Checklist

• Tests added (test/phase.test.ts)
• npm run test:coverage passes locally
• Documented in the README gate table, docs/spec-reference.md and schema/done.schema.json
• CHANGELOG entry under ## Unreleased
• Stays deterministic (no network, no model, no stored state)