fix(acp): use small unique request IDs for Kotlin agents

[StiensWout]

Junie and other agents using the Kotlin ACP SDK reject T3's first core request ID, 2 ** 32, because their decoder accepts only signed 32-bit integers. Initialization then waits until the probe times out.

Core calls and extension requests now allocate IDs from one counter per connection, starting at 1. This removes the separate ID ranges while preserving unique response correlation in both client and agent roles.

Fixes #15263. Alternative to #15374, which lowers the start of the separate core-request range.

Validation: the existing concurrent core/extension request tests now model a signed 32-bit peer. Both fail on main and pass with the fix. Independently reran the client and agent suites, 33 tests, plus package typecheck and targeted lint. The author also ran all 74 effect-acp tests and 246 focused server-consumer tests successfully. One existing lint warning is outside the diff. A real Junie binary was not tested.

_{Prepared for Wout by claude-opus-5-5 in T3 Code's Claude harness. Validated by gpt-6.1-sol in Codex.}

[macroscopeapp]

Approvability

Verdict: Approved at 54c1116

Macroscope's review found this PR approvable — This is a narrowly scoped ACP compatibility fix that unifies per-connection request IDs and keeps them within the range expected by Kotlin agents. Production changes are limited to request allocation and wiring, with focused tests covering uniqueness and signed 32-bit IDs.

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[coderabbitai]

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Reviewing files that changed from the base of the PR and between 245530e and 54c1116.

📒 Files selected for processing: 1

• packages/effect-acp/src/protocol.ts

🚧 Files skipped from review as they are similar to previous changes: 1

• packages/effect-acp/src/protocol.ts

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📝 Walkthrough

The ACP protocol now provides a shared request ID allocator. The agent and client use it for RPC requests. Tests check that RPC and extension request IDs are distinct signed 32-bit integers.

Changes: ACP request ID generation

Layer / File(s)	Summary
Protocol request ID counter packages/effect-acp/src/protocol.ts	AcpPatchedProtocol exposes nextRequestId(). The protocol uses an incrementing connection-local counter for this function and for sendRequest.
Typed RPC ID wiring and checks packages/effect-acp/src/agent.ts, packages/effect-acp/src/client.ts, packages/effect-acp/src/agent.test.ts, packages/effect-acp/src/client.test.ts	The agent and client get RPC request IDs from the protocol. Tests check that RPC and extension IDs are distinct and within signed 32-bit range.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix · Severity of issue fixed: Medium

Merge Risk: ⚪ Minimal · up to 54c11

This change makes ACP request IDs small and unique per connection, which should let Kotlin-based agents such as Junie respond to the first request. No merge-blocking risk was identified. The real Junie binary was not tested.

Security architecture risk: ⚪ Minimal · up to 24553

The change improves compatibility without expanding access or privileges. No introduced security issue was identified, and request correlation remains isolated to each connection.

Retained concerns
No architecture-level concerns identified.

Security review details

Security Blast Radius

• inferred — The changed mutable state affects outbound request correlation on one ACP connection. The inspected change does not introduce cross-connection state sharing or additional peer authority.

Trust Boundaries and Controls

• inferred — A connected peer controls incoming response IDs, but the response-routing boundary is unchanged. Shared unique outbound IDs prevent normal typed/raw collisions; request IDs remain correlation values rather than credentials or authorization checks.

Resilience and Maintainability Implications

• observed — Raw pending entries are removed on response completion, outgoing-send error, and interruption while awaiting a response. Connection termination fails remaining pending work, and writer failure triggers termination. These containment mechanisms are unchanged by the allocator change; RpcClient-internal cleanup was not available for inspection.

Hardening Proposals

• proposed — For a strict connection-lifetime int32 guarantee, define exhaustion behavior explicitly, such as rejecting further allocation and renewing the connection. Any rollover policy should avoid reusing IDs associated with outstanding or delayed responses.

Pre-merge checks: 4

Passed checks: 4 passed

Check name	Status	Explanation
Title check		The title is concise, specific, and accurately describes the main ACP request-ID change for Kotlin agents.
Description check		The description clearly explains the problem, the shared request-ID allocation change, the linked issue, validation results, and the remaining limitation that a real Junie binary was not tested. It do…
Linked Issues check		[#15263] The PR removes the separate core-request counter that started at 2 ** 32. AcpClient.make and AcpAgent.make now obtain IDs from transport.nextRequestId(). makeAcpPatchedProtocol allo…
Out of Scope Changes check		The changes are limited to packages/effect-acp. The protocol adds the shared request-ID allocator, the client and agent use it for core requests, and the related tests verify uniqueness and signed 3…

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[coderabbitai]

Actionable comments posted: 1

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• 🪄 Fix comments: Fix CodeRabbit comments on this PR

🤖 Prompt to fix review comments

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Inline comments:
Review comments at @packages/effect-acp/src/protocol.ts:
- Around line 232-233: Update the nextRequestId allocator to fail before
incrementing once the signed 32-bit request-ID limit is reached, so it never
emits an out-of-range ID. Keep the counter scoped to the protocol instance and
signal exhaustion with an error.

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📥 Commits

Reviewing files that changed from the base of the PR and between 7ac952c and 245530e.

📒 Files selected for processing: 5

• packages/effect-acp/src/agent.test.ts
• packages/effect-acp/src/agent.ts
• packages/effect-acp/src/client.test.ts
• packages/effect-acp/src/client.ts
• packages/effect-acp/src/protocol.ts

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Dismissing prior approval to re-evaluate 54c1116