fix(skills): narrow welcome kickoff routing

[baixiaohang]

Summary

• restrict first-tree-welcome activation to the exact onboarding opener pairs or the explicit production-scan fix sentence
• keep the OpenAI skill metadata and both generated AGENTS routing rows aligned with that contract
• separate model-backed eval activation into auto-trigger, auto-ignore, and preloaded modes
• add positive routing gates for admin, invitee, and greeting-free scan-fix, plus negative gates for ordinary chat and tree setup
• bump first-tree-welcome to 1.2.2

Verification

• python3 scripts/quick_validate_skill.py skills/first-tree-welcome
• pnpm --filter @first-tree/client exec vitest run src/__tests__/agent-briefing.test.ts --maxWorkers=2 --minWorkers=1 (25 passed)
• pnpm --filter @first-tree/skill-evals exec vitest run src/suites/first-tree-welcome/__tests__/floor.test.ts src/suites/first-tree-welcome/__tests__/grader.test.ts --maxWorkers=2 --minWorkers=1 (46 passed)
• pnpm check
• pnpm typecheck
• git diff --check

Model-backed routing checks with gpt-5.6-sol:

• admin exact opener: passed
• invitee exact opener: passed
• greeting-free scan-fix: passed
• ordinary 你好: passed without reading the welcome skill, accessing repo/tree, or sending a tracked ask
• tree-setup opener: passed without reading the welcome skill
• representative preloaded periodic matrix case: passed

Known unrelated eval limitation

The existing readable-repo-populated-tree live case can still fail its exact evidence-snippet matcher even when the model reads both repo and tree evidence and emits three valid task options. This PR does not broaden into that non-routing matcher.

[yuezengwu]

Reviewed the routing contract and eval changes end to end. The welcome skill now activates only for the paired admin/invitee kickoff copy or the explicit scan-fix handoff, while ordinary and tree-setup chats remain negative routing cases. The SKILL.md frontmatter, OpenAI metadata, both generated briefing rows, and the preloaded/auto-trigger/auto-ignore eval split are consistent.

No blocker found. No database, schema, or core data-structure changes are involved.

Locally verified:

• python3 scripts/quick_validate_skill.py skills/first-tree-welcome
• client agent-briefing tests: 25 passed
• welcome floor/grader tests: 46 passed
• pnpm typecheck
• pnpm check (passes; only existing unrelated warnings/info)
• git diff --check

[yuezengwu]

Reviewed the synchronized head 6fdb3706.

The incremental change removes the remaining briefing drift risk by rendering both mutually exclusive First Tree family maps from one shared welcome-routing definition, and the new client test binds each rendered row to the shipped SKILL.md frontmatter. The implementation is safe: the constant is initialized before any exported briefing builder can call the helper, and both tree-less/tree-bound output paths are covered.

No code-level blocker found. No database, schema, or core data-structure changes are involved.

Locally verified on this head:

• python3 scripts/quick_validate_skill.py skills/first-tree-welcome
• client agent-briefing tests: 26 passed
• welcome floor/grader tests: 46 passed
• targeted Biome check
• pnpm check (passes; only existing unrelated warnings/info)
• pnpm typecheck
• incremental git diff --check

One merge prerequisite remains: GitHub currently reports this PR as conflicting with main after #1590. When resolving packages/client/src/runtime/agent-briefing.ts, preserve #1590's readable-source / same-chat Phase 2 wording for both first-tree-seed rows, while keeping this PR's shared ${welcomeRow} rendering. The branch-side older seed wording should not win the conflict. The resolved head should be rechecked after synchronization.