Isolate reviewer CLIs from project autoload; add per-model timeout

[selyafi]

Two hardening fixes to the model-invocation path, both surfaced by reviewing the external xdev skill against diffsmith's adapters. No review-quality change — these are safety, reliability, and determinism.

diffsmith-4tz — isolate reviewer CLIs from project autoload

Reviewer CLIs ran in the caller's cwd, where codex autoloads .agents/skills/*/SKILL.md and can activate a project skill whose workflow posts review comments, and gemini/claude onboard from AGENTS.md / CLAUDE.md. Reviewing a repo that ships such a skill could silently break diffsmith's no-auto-post guarantee.

• New provider.IsolatedRunner() runs each command in a fresh, per-call temp dir (removed after).
• codex/gemini/claude New(nil) defaults now use it. The diff is piped via stdin, so reviewers need no cwd access; $HOME-based auth/config is untouched.
• DefaultRunner (now sharing runCmd) keeps inheriting cwd for gh/glab, whose inbox flow's repo detection needs it.
• Deviation from the issue: dropped codex --ignore-rules — in an empty temp cwd there's no project .rules to ignore, and hard-coding the flag would break reviews on codex versions that don't recognize it.

diffsmith-ptr — per-model wall-clock timeout

Models run in a parallel fan-out that joins on all of them, so one hung reviewer CLI (e.g. an MCP cold-start) blocked the whole review with no recovery.

• Each goroutine's Review now runs under its own context.WithTimeout, so a slow model is cancelled and dropped while siblings finish.
• The same cap guards the synthesis call: a hung lead model surfaces as a synthesis skip reason, never a silent fallback.
• New --model-timeout flag (default 10m; 0 disables). Cancellation reaches the child via exec.CommandContext.

Tests

TDD-first, each RED observed before GREEN:

• IsolatedRunner runs in / cleans up a temp dir (not the caller's cwd).
• A slow model times out while a fast one succeeds.
• Synthesis times out as a skip.

Full suite + go vet + go test -race green.

🤖 Generated with Claude Code