docs(changelog): backpressure, shared SSE fan-out, graceful drain release

[indykish]

Summary

New Jun 11 changelog entry for the usezombie API hardening release (VERSION 0.38.0): in-flight 429 ceiling with rate-limit headers, Server-Sent Events (SSE) stream cap + 503, shared per-instance Redis subscription fan-out with drop-oldest queues, bounded shutdown drain, operator stream listing, signing-key-rotation auth fix, runner lease-deadline kill fix, tear-free telemetry writes.

Pairs with agentsfleet/agentsfleet#393 — merge after (or together with) that PR so the changelog never leads the code.

🤖 Generated with Claude Code

Greptile Summary

Adds a new <Update> block for Jun 11, 2026 documenting the 0.38.0 API hardening release: in-flight request ceiling with 429/Retry-After, per-instance SSE stream cap with 503, shared Redis subscription fan-out, bounded shutdown drain, signing-key rotation fix, and runner lease-deadline kill fix.

• All previously flagged terminology is resolved — bare product-noun "zombie" was replaced with "agent"; exempt code tokens (zombie_sse_* metrics, /v1/zombies/{id}/… paths) are correctly left in place.
• Section order (What's new → API reference → Bug fixes), date format (MMM DD, YYYY), sentence-case headings, and code-formatted env vars all conform to the AGENTS.md style guide.
• Two same-date entries carry distinct titles as required when dates collide.

Confidence Score: 5/5

Documentation-only change adding a single changelog entry; no code, schema, or configuration is modified.

The change is a single Update block in a Mintlify MDX file. Terminology, section order, date format, and code-token exemptions all conform to the style guide. The previously flagged bare product-noun was fixed in the head commit. No functional code is touched.

No files require special attention.

Important Files Changed

Filename	Overview
changelog.mdx	New Jun 11, 2026 Update block documenting backpressure, shared SSE fan-out, and graceful drain; terminology, section order, and date format all correct.

Sequence Diagram

sequenceDiagram
    participant Client
    participant API
    participant SSEHub
    participant Redis

    Note over API: in-flight >= API_MAX_IN_FLIGHT_REQUESTS
    Client->>API: POST /v1/...
    API-->>Client: "429 Retry-After + X-RateLimit-* (UZ-API-001)"

    Note over API: SSE streams >= SSE_MAX_STREAMS
    Client->>API: "GET /v1/zombies/{id}/events/stream"
    API-->>Client: 503 Retry-After (UZ-API-002)

    Note over API: Normal SSE fan-out (shared subscription)
    Client->>API: "GET /v1/zombies/{id}/events/stream"
    API->>SSEHub: Join per-instance hub
    SSEHub->>Redis: One shared subscription (if not already open)
    Redis-->>SSEHub: Agent frames
    SSEHub-->>Client: SSE frames (bounded per-viewer queue)

    Note over API: Shutdown drain
    API->>SSEHub: Reject new streams, wake live ones
    SSEHub-->>Client: Stream closed (bounded window)

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_{Reviews (2): Last reviewed commit: "docs(changelog): zombie -> agent product..." | Re-trigger Greptile}

Context used:

• Context used - AGENTS.md (source)

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Project	Status	Preview	Updated (UTC)
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