Web pipeline: retrieval rides with discovery; hallucinated fetch calls get steered

[jjang-ai]

Why

A model with web search enabled saw only web_search (discovery) in its schema; retrieval (search_and_extract) sat behind a capabilities_load round-trip. Observed live: models loop-rephrased web_search or hallucinated web_fetch — a tool that has never existed in osaurus — and produced zero page reads (the Raptor research-run failure).

What

1. search_and_extract is composed into the schema whenever web search is enabled (was: Charts+Web combo or orchestrator only). The web-off strip still removes both halves; manual mode untouched. Cost: ~350–420 tokens on web-enabled prompts — the same spec the Charts+Web path already paid.
2. web_search's description names the direct transition ("search_and_extract IS the fetch tool") and drops the capabilities_load detour — on the Default agent that loader is gated to configure writes, so the old text steered into a rejected load. Same fix in the web_search anti-loop nudge.
3. Hallucinated fetch names get steered, not dead-ended: web_fetch/fetch_url/read_webpage/… return a retryable envelope pointing at search_and_extract — only when the name has no real registration (a plugin/MCP tool claiming it always wins), the request's scope already exposes search_and_extract (nothing withheld is leaked; nil-scope HTTP/MCP surfaces keep the generic refusal), and no plugin group shares the name (group-load rescue keeps precedence). Browser-intent (browse, open_url) and shell-intent (curl) names are deliberately excluded.

Verification

• Adversarial audit of the diff (leak/shadowing/precedence/envelope-keys): steering can never name a tool outside the request's own scope; toolsByName guard keeps real registrations winning; group rescue precedence guarded; envelope keys verified against ToolEnvelope.failure.
• Tests: composer exposure both ways (web on → both halves; web off → neither), steering + opacity contracts in ToolScopeGateRecoveryTests, superseded lean-baseline pin updated, description contract test updated.
• Release build clean.