fix(acp): registry agents that advertise /compact can run it

[Mnigos]

Fixes #16663

Problem

The composer offers Compact (and accepts /compact) for any ACP registry agent that advertises a compact slash command, such as Devin. The registry adapter never set supportsCompaction, so its sessions had no compactThread, and a bare /compact failed with ProviderAdapterTurnStartError before session/prompt was ever sent. Thanks to @stilak12 for the precise diagnosis and the attachment workaround in the issue.

Change

• AcpRegistryAdapterV2.ts: the registry flavor sets supportsCompaction: "advertised", so /compact goes to the agent through session/prompt, the same path Grok and Antigravity use, but only for agents that advertise a compact command.
• AcpAdapterV2.ts: after a completed /compact turn, the adapter adds a synthetic "Context compacted" row. Agents that report compaction_update already produce a compaction row ("Compact context"), so turning the flag on alone shows two compaction rows (the new test caught this). The synthetic row is now skipped when the turn already has an acp-compaction: item. A successful /compact response without a native compaction update still gets the synthetic row. Grok and Antigravity keep their current behavior; if they start sending compaction_update, they will show one row instead of two.
• The synthetic row and the /compact route are gated on the agent's advertised commands, because RunExecutionService routes every bare /compact to compactThread, including one typed by hand to an agent that has no compact command. The ACP adapter now records each session's available_commands_update. With "advertised", /compact fails with the existing "This provider does not support context compaction." error when the session advertised commands without compact, and the synthetic "Context compacted" row appears only when compact was advertised. If the agent has not advertised any commands yet, /compact is still sent, but no synthetic row is added unless compact is advertised before the turn ends. Grok and Antigravity keep supportsCompaction: true and are unchanged.

Verification

Gate	Result
vp test run src/orchestration-v2/Adapters/AcpRegistryAdapterV2.test.ts src/orchestration-v2/Adapters/AcpAdapterV2.test.ts (apps/server)	2 files, 126/126 passed, exit 0
vp run typecheck (apps/server, packages/provider-acp, packages/provider-acp-registry)	exit 0, 0 error TS / warning TS
vp lint --ignore-path=/dev/null on the 3 changed files	exit 0, 0 errors
vp fmt --stdin-filepath on the 3 changed files	byte-identical

Test cases (scripted ACP registry agent that first advertises its commands, AcpRegistryAdapterV2.test.ts):

Test	Base (main)	Flag only, no row dedupe	This branch
Bare /compact goes through session/prompt and a native compaction_update shows one row	Fails: the registry session has no compactThread, which is why RunExecutionService fails the turn in the issue	Fails: two rows, ["Compact context", "Context compacted"]	Passes: session/prompt leads with /compact, one row: ["Compact context"]
Successful /compact response without a native compaction update shows the synthetic row	Fails: no compactThread	Passes	Passes: ["Context compacted"]
An agent that advertises commands without compact gets no session/prompt and no success row	Fails: no compactThread	Fails: /compact is sent and the turn is treated as a compaction	Passes: compactThread fails with "This provider does not support context compaction." and the transcript has no prompt

The scripted agent's replay matcher checks the outgoing session/prompt for exact keys, array length and order, the session id, and a first text block that is exactly /compact. The second block (T3 Code's runtime context, which main already appends) is matched with <any>, so its content is not checked.

This is a server-only change with no UI, so there are no screenshots.

Limitations / not checked: no real Devin or other ACP registry agent was run. The tests use a scripted ACP replay agent, so they cover the adapter's protocol messages and turn items, not any real agent's /compact handling or actual context reduction. The live events of Grok and Antigravity were not checked. The orchestrator path (RunExecutionService → compactThread) was not run end to end in a live server. The case where /compact arrives before the agent has advertised any commands (for example right after a server restart) is not covered by a test: the prompt is sent and the synthetic row depends on a later advertisement.

Implemented with Claude Opus 5.5, verified with GPT-6 Astra, coordinated by Claude Fable 5.1 in Claude Code.

[macroscopeapp]

Approvability

Verdict: Approved at 06f4282

Macroscope's review found this PR approvable — This is a narrow ACP adapter fix that enables the existing /compact workflow only for sessions advertising the command, while preserving unsupported-agent errors and preventing duplicate compaction rows. Production changes are localized and accompanied by focused protocol-level tests; the remaining changes are test-only.

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📥 Commits

Reviewing files that changed from the base of the PR and between a2b50ad and 06f4282.

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📒 Files selected for processing (3)

• apps/server/src/orchestration-v2/Adapters/AcpRegistryAdapterV2.test.ts
• packages/provider-acp-registry/src/server/adapter.ts
• packages/provider-acp/src/server/adapter.ts

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🚧 Files skipped from review as they are similar to previous changes (3)

• packages/provider-acp-registry/src/server/adapter.ts
• apps/server/src/orchestration-v2/Adapters/AcpRegistryAdapterV2.test.ts
• packages/provider-acp/src/server/adapter.ts

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📝 Walkthrough

📝 Walkthrough

Walkthrough

The ACP Registry adapter now enables compaction based on each agent’s advertised commands. The ACP adapter tracks those commands, routes /compact requests according to the session’s capabilities, and avoids adding a synthetic compaction item when the agent already reported one. Tests cover supported and unsupported cases.

Changes

ACP registry compaction

Layer / File(s)	Summary
Route compaction by advertised capability packages/provider-acp/src/server/adapter.ts, packages/provider-acp-registry/src/server/adapter.ts	The ACP Registry flavor enables advertised compaction support. The ACP adapter records command updates, permits compaction before commands are known, and returns an error when a session explicitly lacks compact.
Handle compaction results packages/provider-acp/src/server/adapter.ts, apps/server/src/orchestration-v2/Adapters/AcpRegistryAdapterV2.test.ts	A successful, attachment-free /compact turn produces a synthetic compaction item only when applicable and when no native item exists. Tests cover native and synthetic items, and the unsupported-command error.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix · Severity of issue fixed: Low

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Merge Risk: ⚪ Minimal · up to 06f42

Registry agents can receive /compact when they advertise support, while sessions that explicitly lack it are rejected. No merge-blocking issue is established; live-agent behavior remains unverified.

Architecture Summary

Architecture risk: 🔵 Low · up to a2b50

The change affects 3 systems.

Changed systems: packages/provider-acp, packages/provider-acp-registry, apps/server

Architecture concerns
No architecture-level concerns identified.

Review details

Systems and components

• observed — packages/provider-acp (library) was modified; 1 changed file maps to changed impact.
• observed — packages/provider-acp-registry (library) was modified; 1 changed file maps to changed impact.
• observed — apps/server (service) was modified; 1 changed file maps to changed impact.

Before / after behavior

• observed — Modified behavior in apps/server/src/orchestration-v2/Adapters/AcpRegistryAdapterV2.test.ts: The test adds imports for message, node, project, and run identifiers used to construct compaction inputs.
• observed — Modified behavior in apps/server/src/orchestration-v2/Adapters/AcpRegistryAdapterV2.test.ts: DateTime is imported for the compaction test's timestamps.
• observed — Modified behavior in apps/server/src/orchestration-v2/Adapters/AcpRegistryAdapterV2.test.ts: Stream is imported to collect runtime events in the compaction test.
• observed — Modified behavior in apps/server/src/orchestration-v2/Adapters/AcpRegistryAdapterV2.test.ts: A /compact test suite defines the scripted session ID and a helper for emitting ACP compaction updates, and documents the replay scenario.

Reliability and maintainability

• inferred — Risk-relevant change factors for packages/provider-acp: blast_radius_1; direct_dependents_1

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Pre-merge checks | 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check		Issue #16663 requires /compact on ACP registry agents that advertise compact to reach session/prompt. The registry flavor now sets supportsCompaction: "advertised". The adapter records `availa…
Out of Scope Changes check		The changes in packages/provider-acp, packages/provider-acp-registry, and the server tests support the registry compaction fix. Synthetic-row deduplication prevents duplicate compaction rows when …
Title check		The title clearly identifies the fix that lets ACP registry agents advertising /compact execute it.
Description check		The description includes the problem, implementation details, linked issue, focused verification results, limitations, and scope information. It is sufficiently complete for review.

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Actionable comments posted: 1

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Inline comments:
Review comments at @packages/provider-acp-registry/src/server/adapter.ts:
- Line 201: Update the `RunExecutionService` compaction flow to check the
registry agent’s advertised commands before calling
`input.session.compactThread` or emitting the synthetic “Context compacted” row;
only proceed when the agent advertises `compact`.

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