fix(server): bound live event buffers for slow clients

[rynfar]

A slow or disconnected client could retain an unbounded queue of live events and exhaust the Pylon server’s memory. Bound each shell/thread subscription to 1,000 items and 8 MiB, including coalesced batches and the batch awaiting acknowledgement. Overflow detaches the producer immediately and returns the existing recoverable stream error so clients resume from their last applied sequence.

Adopts approved B2, upstream #9715, 108f295cc3672716c3cb8291ce487846df5ce098. Preserves Pylon’s startup subscription attachment, replay ordering, deletion recovery and rollback event routing. Authoritative snapshots stay outside the live-event budget. Applies to every provider and web, desktop and mobile, including remote/relay/tunnel connections.

Validation: 166 focused budget, coalescer and WebSocket server tests plus 18 shared client synchronization/error tests pass. Held-ACK tests verify producer cleanup before acknowledgement and exact replay/deletion recovery. Scoped server/client-runtime types, targeted lint and diff checks pass. No live environment state was used.

Model: GPT-6 Astra. Harness: Codex.

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[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

ℹ️ The exact PR base did not have a successful artifact. Baseline uses the latest successful main measurement shown below.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	13.6 KiB	13.6 KiB	−1 B (−0.0%)	15.1 KiB	✅
Codex	Thread snapshot wire	7.1 KiB	7.1 KiB	+2 B (+0.0%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.5 KiB	6.5 KiB	−3 B (−0.0%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	56.5 KiB	56.5 KiB	0 B (0.0%)	66.4 KiB	✅
Codex	Live turn messages	8	8	0 (0.0%)	21	✅
Claude	Total thread wire	13.6 KiB	13.7 KiB	+10 B (+0.1%)	15.1 KiB	✅
Claude	Thread snapshot wire	7.1 KiB	7.1 KiB	+8 B (+0.1%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.6 KiB	6.6 KiB	+2 B (+0.0%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	57.3 KiB	57.3 KiB	0 B (0.0%)	66.4 KiB	✅
Claude	Live turn messages	8	8	0 (0.0%)	21	✅

Baseline: c3fbc15 · PR result: ced82a3 · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 111.2 KiB
• Claude decoded thread snapshot: 111.9 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.