fix: make a brokered Grok worker actually run, and make its failures diagnosable

[apresmoi]

Makes a brokered Grok worker run end to end under Daimon inside a training container, and makes every failure name its own cause.

What was broken

• the broker MCP facade dropped Mcp-Session-Id, so every mounted tool was unreachable and search_tool returned an empty catalogue
• the worker's stdout pipe was non-blocking on the child's end, killing it with EAGAIN on its first large write
• DBL_MAX_OUTPUT (64 KiB) was exceeded by an ordinary turn, and the trip discarded the turn's whole text
• a failed worker's own words were erased in three separate layers, so exit=1 was unexplainable by construction
• an expired credential was retried ~15 times instead of being named

What this adds

• MCP session/protocol header forwarding plus GET/DELETE, with a closed allowlist
• a blocking child pipe with a non-blocking launcher read end, and a no-hang proof
• the output bound raised to the protocol's own text bound (262,144), set on measurement
• the worker's last words captured head + elision marker + tail, redacted, inside the sealed terminal response
• per-request tool-call names, an MCP call and tunnel observation, and a turns.jsonl seal ledger that survives a hung turn
• auth_stale as a named non-retryable refusal; policy misses answered 400 rather than blind-retried 503
• an inbox turn leads with the delivery's own text; Grok tool names render as daimon__<name> from shared contract atoms
• the MCP capability budget derived from the compiled turn bound so the two cannot drift
• the v2 activity closure query stays answerable after a control host stop

Verification

Full suite 887 pass / 0 fail. Typecheck, contract manifest, production closure and native verify all green. The Docker native adversarial suite passes all 16 stages, including a real 219,608-byte turn and a no-hang proof where the worker is asleep inside write().

Reviewed adversarially before this PR; every blocking finding was fixed with a failing-first test and a named mutation check.

🤖 Generated with Claude Code