test(coding-agent): prove B00B production-path swarm gate

[sethkarten]

Outcome

Adds the B00B test-only production-path gate on top of C00. It exercises real provider registration, AgentSession.runRlmChild, daemon supervisor/workers, upstream cancellation/429 handling, signed evidence, exact economics, attachment backpressure, and whole process-group RSS without changing production behavior.

Stack: #1106 → #1107 → this PR.

Scope boundary

• Diff is confined to 16 files under packages/coding-agent/test/swarm.
• No production src, provider default/export, dependency, daemon protocol, product documentation, shared semaphore, client queue, local 429, or paid/network provider.
• Independent requests enter the scripted provider concurrently; barriers observe entry and never admit/rate-limit requests.
• This is a reproducibility/resource-safety gate, not an absolute RSS improvement claim.

Exact validation

Exact head 9d9cf28d51490ef06efba738c3fff788463acdff on the pinned isolated Linux runner:

• Biome and root tsgo --noEmit: pass
• Full monorepo build: pass
• Integrated focused suite: 70/70
• Real RLM + signed-adapter suite across three invocations: 60/60
• Process-stress: 6/6 runnable, 8 tag-skipped
• RSS fanout 1/4/16/64 × 5: 20/20 complete, max gap 28 ms, positively verified final empty process groups
• No surviving matching processes, sockets, or temp directories

Retained evidence archive SHA-256: f9985c73eecc893904e4c5d40958d34e964b44295895a43481a1bee4552c871c
Exact Git bundle SHA-256: 2d06070c9411a9c729b5c2e2513ce3f661d84ec313ac70f87200ea3939698359

Evidence integrity

A retained content-free corpus is externally Ed25519 committed and fresh-process verified. Artifact/trust files are 0600; recursive privacy scans reject fixture canaries. Requested/resolved identities and exact integer economics remain separate. Failed historical RSS/cadence/ownership campaigns remain retained in the component evidence history.

Merge order

Review the complete stack now, but merge parent-first: #1106, then #1107, then this PR. Revalidate each updated head/default branch before advancing.

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