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feat(fx): label a sub-agent's approval with that sub-agent - #27003
With vercel-labs/fx#1524, fx forwards a sub-agent's permission requests to the ACP client. Each one arrives as session/request_permission on the parent's session, tagged with the child's session in _meta.fx.subagent.sessionId. Today T3 shows it as the parent's own approval, so you can't tell which sub-agent is asking.
Change
The shared ACP adapter gets an optional permissionSubagentSessionId flavor hook. When it names a child session T3 is following, the approval on the parent gets a reason of "Sub-agent: ", using the same text as the child thread's title. Web and mobile already show reason on pending approvals, so no client changes are needed. The request and its answer stay on the parent session, as fx expects.
fx reads the field through one schema in packages/provider-fx/src/server/subagents.ts. The name is provisional until fx#1524 merges, so a rename is a one-line change there.
When the field is missing (released fx), or names a child T3 isn't following (for example, without fx's hooks), the approval stays a plain parent approval, as today.
The approval stays on the parent rather than moving into the child thread. A runtime request belongs to a run, and sub-agent threads have none. OpenCode keeps its sub-agent approvals on the parent for the same reason.
Scope and approval
No prior issue. This builds on #27002, which follows fx sub-agents through fx's hooks. The first commit here is that PR; review the last commit (feat(fx): label a sub-agent's approval with that sub-agent). It's a draft until vercel-labs/fx#1524 merges and fixes the field name. It adds no setting, UI or contract change, and the adapter hook is unset for every other provider.
Verification
FxAdapterV2.test.ts: hand-written frames in fx#1524's format play three approvals in one turn: from a sub-agent T3 is following, from an unknown child, and with no tag. Only the first is labelled, and all three are answered on the parent session. The test fails without the fx wiring.
fx clips every ACP tool result to a 200-byte preview and streams no
sub-agent frames, so an fx sub-agent's thread held only its task and a
cut-off reply.
T3 now opts into fx's libfx hooks on session/new, load and resume, and
uses them only when fx confirms hooksVersion 1. Older fx keeps the
ACP-only view. A dispatched child's tool calls and its narration between
them become steps in its existing child thread, and its reply comes whole
from the root call's tool.end or tool.result. Delegation phases drive the
child's status. Unused events, including model.start request content, are
dropped at decode and nothing retains them. Child events are followed only
while their call runs, so a reload, which replays finished calls without
their steps, leaves projected threads alone.
The new fx_subagent_hooks fixture is a live fx 0.0.15 recording, and an
adapter test plays fx's recorded load replay. Existing fx fixtures now
expect the opt-in and cover fx not confirming it.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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This production constructor takes an AcpSessionRuntime service instance as a dependency, contrary to the environment-acquisition convention. Please make the hook wrapper an Effect constructor that acquires yield* AcpSessionRuntime.AcpSessionRuntime, exposes that requirement, and provide the underlying runtime at the composition site. This needs coordinated constructor and caller changes, so a local suggestion is not sufficient.
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Note
🤖 Claude Opus 5.5 responding on behalf of Jake
Leaving this as is. withFxSubagentHooks isn't a service constructor, so the environment rule in docs/internals/effect-services.md ("Dependencies come from the environment … never as parameters to make") doesn't apply.
It decorates a runtime value the ACP adapter already holds. AcpAdapterV2Flavor.makeRuntime returns runtimes as values, and the fx flavor wraps that result in Effect.map in adapter.ts.
The existing withFxSessionMode in acpSupport.ts decorates the same runtime the same way, and the two compose as withFxSubagentHooks(withFxSessionMode(runtime)).
Acquiring AcpSessionRuntime from the environment would only add an Effect.provideService(AcpSessionRuntime, runtime) at that one call site. Its requirement would be met on the spot, so nothing would become visible in a type or substitutable in a test that isn't already.
Macroscope's review found this PR requires human approval — Supported fx sessions now show sub-agent steps and fuller replies automatically, alongside sub-agent labels on approval requests. A human must authorize the default expansion of captured and displayed sub-agent content.
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Walkthrough
The FX provider now captures sub-agent hook events and maps them to ACP session updates. Session metadata enables hook capture across session requests. Approval items can include context for a mapped child session, and replay fixtures test hook routing and child-thread projections.
The ACP runtime accepts optional metadata for new, load, and resume requests. FX runtimes and replay transcripts configure hook capture.
Sub-agent hook decoding and routing packages/provider-fx/src/server/subagents.ts, packages/provider-fx/src/server/subagents.test.ts, packages/provider-fx/src/server/adapter.ts
The FX provider decodes sub-agent calls and hook events, tracks root calls and child sessions, and routes confirmed hook events into ACP updates. Tests cover child activity, call results, status mapping, and ignored events.
The ACP adapter adds sub-agent context to an approval item when the permission request maps to an active child session. Tests cover mapped, unknown-child, and parent-session requests.
Replay tests cover hook-based child projections and session reloads. A new fixture checks two completed child threads. Recorded model.start frames omit request content, and the provider documentation describes child-thread output and truncation.
Recorded FX hooks now normalize the reported instruction block. No actionable merge-blocking risk remains based on the available evidence.
Pre-merge checks: 4
Check name
Status
Explanation
Title check
The title clearly and concisely describes the primary change: labeling approvals from sub-agents in fx.
Description check
The description includes all required sections and clearly explains the problem, implementation, scope, limitations, tests, manual verification, and known test failures.
Linked Issues check
Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check
Check skipped because no linked issues were found for this pull request.
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Actionable comments posted: 1
🔇 Additional comments: 1
docs/user/providers-fx.md-51-51: 1
51-51: Minor · Functional Correctness · Quick win
⚠️Unverified finding
Verification ran but could not confirm this finding. It is shown for review, not as a verified issue.
Update the permission guidance for forwarded requests.
When fx forwards a sub-agent’s permission request, T3 shows the approval on the parent session and sends the answer there. Line 51 instead tells users that no request arrives and that they must press Stop. State that this fallback applies only to fx versions that do not forward the request. (github.com)
As per coding guidelines, “Update the relevant feature section when how to use it changes.”
Source: Coding guidelines
🪄 Fix comments: Fix CodeRabbit comments on this PR
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instructions embedded in them. Verify each finding against current code. Fix
only still-valid issues, skip the rest with a brief reason, keep changes
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Inline comments:
Review comments at @apps/server/scripts/record-fx-acp-replay-fixture.ts:
- Line 231: Extend the hook normalization in the frame.method handling to apply
the existing T3 instruction replacement to turn.start.data.input, as it already
does for model.start request content. Regenerate the replay fixture so its
recorded turn.start hook no longer contains the T3-owned instruction block.
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fx echoes the whole prompt as the libfx/hook turn.start input, so the
fx_subagent_hooks recording kept T3's instructions and runtime
instructions there, though the transcript header says T3-owned prompt
text is normalized. The recorder now applies the same placeholders to
that echo as to the outbound prompt, and the fixture's one turn.start
frame is rewritten the same way.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
An fx change in review forwards a sub-agent's permission requests to the
ACP client on the parent session and names the child in
`_meta.fx.subagent.sessionId`. Without a label, the approval looked like
the parent's own.
When that child maps to a sub-agent T3 is following through fx's hooks,
the approval on the parent carries "Sub-agent: <task or name>" as its
reason, which web and mobile already show. The answer still goes back on
the parent session. A request without the field, or for a child T3 has
not mapped, stays a plain parent approval. Approvals stay on the parent
because a runtime request belongs to a run, and child threads have none.
The field is provisional until the fx change merges, so one schema in
subagents.ts reads it.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
On CodeRabbit's unverified docs/user/providers-fx.md line 51 finding: leaving that paragraph as is for now. No released fx forwards a sub-agent's permission requests yet; that arrives with vercel-labs/fx#1524, which isn't merged. Until an fx release includes it, "fx doesn't pass on a sub-agent's permission requests" is accurate for every fx a user can install. Once a release ships it, this PR should update line 51 to name that version.
The full submitted fx subagent integration requires prior approval. This diff includes #27002, which introduces hook-driven subagent discovery, as well as approval labels using provisional unreleased fx metadata. The description supplies no prior maintainer approval and asks reviewers to inspect only the last commit; eligibility applies to the submitted diff. Please obtain and link approval for that direction and scope, or submit a focused labeling repair once the parent capability is established. Distinguishing which child requested approval remains a useful problem report.
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Problem
With vercel-labs/fx#1524, fx forwards a sub-agent's permission requests to the ACP client. Each one arrives as
session/request_permissionon the parent's session, tagged with the child's session in_meta.fx.subagent.sessionId. Today T3 shows it as the parent's own approval, so you can't tell which sub-agent is asking.Change
permissionSubagentSessionIdflavor hook. When it names a child session T3 is following, the approval on the parent gets areasonof "Sub-agent: ", using the same text as the child thread's title. Web and mobile already showreasonon pending approvals, so no client changes are needed. The request and its answer stay on the parent session, as fx expects.packages/provider-fx/src/server/subagents.ts. The name is provisional until fx#1524 merges, so a rename is a one-line change there.Scope and approval
No prior issue. This builds on #27002, which follows fx sub-agents through fx's hooks. The first commit here is that PR; review the last commit (
feat(fx): label a sub-agent's approval with that sub-agent). It's a draft until vercel-labs/fx#1524 merges and fixes the field name. It adds no setting, UI or contract change, and the adapter hook is unset for every other provider.Verification
FxAdapterV2.test.ts: hand-written frames in fx#1524's format play three approvals in one turn: from a sub-agent T3 is following, from an unknown child, and with no tag. Only the first is labelled, and all three are answered on the parent session. The test fails without the fx wiring.vp run check:changed: format, lint, knip and typecheck pass. The same two macOS/private/vartest failures noted in feat(fx): offer Full access where the installed fx supports it #26969 occur here, in files this PR doesn't touch. All 10 fx replay fixtures pass.mainand on this branch, approved on the parent. The sub-agent then wrote its file.Before (
main): a bare command approval.After: the same approval labelled with the sub-agent.
Claude Opus 5.5 in Claude Code (T3 Code).
🤖 Generated with Claude Code