fix: expose session.subscribe on ACP runtime sessions for engine workflow steps - #3501
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Included review availability: Your plan provides up to 4 included reviews per hour; 0 remain after this review. 📝 WalkthroughWalkthroughThe ACP runtime adapter adds engine-compatible session subscriptions, replays streamed ACP events as pi-shaped events, preserves existing callbacks, isolates subscriber failures, supports unsubscribe cleanup, and merges task-scoped environment values into allowed subprocess variables. ChangesACP session compatibility
Lane wiring maintenance
Estimated code review effort: 3 (Moderate) | ~20 minutes Merge Risk: 🟡 Moderate · up to The PR is not merge-ready while duplicate declarations prevent TypeScript compilation, and the new session event bridge still carries a bounded risk of incorrect downstream handling of streamed output until its event contract is confirmed or corrected. Sequence Diagram(s)sequenceDiagram
participant ACPClientHandler
participant ACPRuntimeSession
participant Subscriber
participant ExistingCallbacks
ACPClientHandler->>ACPRuntimeSession: stream text, thinking, or tool event
ACPRuntimeSession->>Subscriber: emit pi-shaped event
ACPRuntimeSession->>ExistingCallbacks: invoke existing callback
Subscriber-->>ACPRuntimeSession: return or throw
ACPRuntimeSession->>ACPRuntimeSession: isolate subscriber exception
🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
✨ Finishing Touches🧪 Generate unit tests (beta)
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| Filename | Overview |
|---|---|
| plugins/fusion-plugin-acp-runtime/src/runtime-adapter.ts | Adds session subscription replay, cleanup, dual callback delivery, and allow-listed task environment forwarding without an eligible blocking issue. |
| plugins/fusion-plugin-acp-runtime/src/types.ts | Extends ACP runtime options and sessions with the task environment and subscription contracts implemented by the adapter. |
| plugins/fusion-plugin-acp-runtime/src/tests/runtime-adapter.test.ts | Covers pi-shaped event replay, handler-specific unsubscription, and simultaneous callback and subscriber delivery. |
| .changeset/acp-session-subscribe-compat.md | Uses the supported fix category, resolving the previously reported changeset-format concern. |
| scripts/lib/lane-wiring-baseline.json | Updates the lane-wiring baseline with the current self-healing call-site count. |
Sequence Diagram
sequenceDiagram
participant Engine
participant Session as ACP Session
participant Bridge as ACP Event Bridge
participant Callback
participant Subscriber
Engine->>Session: subscribe(handler)
Session-->>Engine: unsubscribe()
Bridge->>Callback: text/thinking/tool event
Bridge->>Subscriber: pi-shaped event
Engine->>Session: dispose()
Session->>Session: clear subscribers
Reviews (6): Last reviewed commit: "fix: expose session.subscribe on ACP run..." | Re-trigger Greptile
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Inline comments:
In `@plugins/fusion-plugin-acp-runtime/src/__tests__/runtime-adapter.test.ts`:
- Line 129: Remove the duplicate lexical declarations in the test, retaining
exactly one events declaration near the event collection logic and exactly one e
declaration near its usage. Preserve the existing types and behavior while
ensuring TypeScript accepts the scope.
- Around line 163-185: Expand the “keeps original callbacks firing alongside
subscriber replay” test to register and collect the existing onThinking,
onToolStart, and onToolEnd callbacks, then assert the subscriber receives
matching events for each surface alongside the original callback results.
Preserve the current onText assertion and use the adapter’s established event
types and callback payloads.
In `@plugins/fusion-plugin-acp-runtime/src/types.ts`:
- Around line 119-120: Update both newly added comment blocks with the required
FNXC area prefix and UTC timestamp. Correct the subscribe/unsubscribe contract
near subscribe so it states that subscribe returns an unsubscribe function that
removes the registered handler, rather than describing unsubscribe as a no-op.
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Inline comments:
In `@plugins/fusion-plugin-acp-runtime/src/__tests__/runtime-adapter.test.ts`:
- Around line 130-158: The runtime adapter subscription test should verify
handler-specific unsubscription rather than merely checking that a failed prompt
emits nothing. In the test around session.subscribe and promptWithFallback,
register a second subscriber whose handler remains retained, require the second
prompt to resolve successfully, and assert that only the unsubscribed handler
receives no additional events while the retained handler continues receiving
events.
In `@plugins/fusion-plugin-acp-runtime/src/runtime-adapter.ts`:
- Around line 84-96: Update the event handling around the onText and onThinking
callbacks so contentIndex remains unchanged for all deltas within the current
content block, incrementing it only when a new content block begins. Preserve
the existing delta-only message_update shape, including omitted partial and
top-level message fields.
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Actionable comments posted: 1
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Inline comments:
In `@plugins/fusion-plugin-acp-runtime/src/__tests__/runtime-adapter.test.ts`:
- Around line 138-146: Strengthen the runtime adapter test around the text_delta
and thinking_delta events by emitting multiple deltas for each content block and
asserting that every delta in each block retains the same contentIndex. Update
the event assertions near textDelta and thinkingDelta to validate the invariant
across all emitted deltas, not just that one event of each type exists.
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…flow steps The engine's AgentSession contract (pi-coding-agent) exposes subscribe(handler) and two production call sites call it unconditionally: execute-workflow-step.ts (Plan/Code Review steps) and pi.ts fallback wiring. ACP sessions streamed through the bridging client handler onto callbacks instead, so any workflow step executed by an ACP agent (Hermes/Prime/Grok) crashed before producing a verdict with 'session.subscribe is not a function'. - wrap raw callbacks so forwarded text/thinking/tool events are also replayed to subscribers as pi-shaped events (message_update + assistantMessageEvent) - expose session.subscribe(handler) returning an unsubscribe function - merge engine taskEnv into the subprocess env behind the allow-list boundary - regression tests: event replay, unsubscribe, dual delivery (echo-agent fixture)
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## Summary - normalize callback-only plugin sessions at the shared runtime boundary - preserve runtime-native subscriptions and isolate subscriber failures - strengthen ACP multi-delta, unsubscribe, and callback-delivery coverage - correct the task environment and unsubscribe contracts ## Why PR #3501 fixed the generic ACP adapter, but workflow steps still call `session.subscribe()` unconditionally. Bundled callback-only runtimes such as Hermes and the vendored Grok/Claude/OMP ACP clients can still return sessions without that method. Handling the compatibility once in `createResolvedAgentSession` closes every current runtime surface without copying the bridge into each adapter. ## Testing - `packages/engine`: `agent-session-helpers.test.ts` — 61 passed - `fusion-plugin-acp-runtime`: `runtime-adapter.test.ts` — 14 passed - `fusion-plugin-acp-runtime`: `process-manager.test.ts` — 15 passed - engine typecheck passed - ACP runtime typecheck passed - changeset format, FNXC date check, ESLint, and `git diff --check` passed <!-- This is an auto-generated comment: release notes by coderabbit.ai --> ## Summary by CodeRabbit - **Bug Fixes** - Improved compatibility with callback-based runtime sessions. - Added reliable subscriptions for text, thinking, and tool activity updates. - Preserved native subscription behavior where available. - Prevented subscriber errors from interrupting event delivery. - Improved unsubscribe behavior for removed handlers. - Improved event delivery during deferred runtime fallback. - Corrected task environment values passed to runtime subprocesses. - **Tests** - Expanded coverage for streaming updates, fallback handling, cleanup, and subscriber isolation. <!-- end of auto-generated comment: release notes by coderabbit.ai -->
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Summary
Fixes the
session.subscribe is not a functioncrash that breaks every engine workflow step (Plan Review, Code Review) executed by an ACP agent (Hermes ACP, Prime, Grok).Introduced by the ACP custom-tools bridge (#3476) in the sense that it made the gap reachable: ACP sessions stream through the bridging client handler onto
callbacksand never exposed the pi-stylesubscribe()that the engine's AgentSession contract promises. Two production call sites call it unconditionally:packages/engine/src/executor/execute-workflow-step.ts(workflow steps — Plan Review / Code Review)packages/engine/src/pi.tsfallback wiring (wireFallbackHooks,promptableSession.subscribe)(
reviewer.tsguards withtypeof session.subscribe === "function"; the other paths do not.)Real-world symptom (verified on 0.77.0-beta.6 with a Hermes ACP agent): every Plan Review attempt fails before producing a verdict:
Fix
Fix at the seam rather than guarding every call site forever:
AcpRuntimeAdapter.createSessionwraps the raw callbacks so each forwarded text/thinking/tool event is also replayed to subscribers as the pi-shaped event consumers parse (message_update+assistantMessageEvent.{text_delta,thinking_delta},tool_execution_start/end)session.subscribe(handler)returning an unsubscribe function; dispose clears subscriberstaskEnvinto the subprocess env behind the existing allow-list trust boundary (KTD6b preserved — only allow-listed keys forward, task values win)Testing
New regression tests in
runtime-adapter.test.tsagainst the real echo-agent fixture (ACP_FIXTURE_RICH_PROMPT=1):onTextcallback AND subscriber both fireFull plugin suite: 255 passed (21 files)
tsc --noEmitclean for the pluginchangeset for
@runfusion/fusion(patch, bugfix)Summary by CodeRabbit
New Features
Bug Fixes