fix(mobile): scope child session error to the child sheet

[iscekic]

Summary

• A subagent failure now appears only in the failed subagent's sheet, not on the main session screen.
• The main session's composer stays clear of a subagent's error.
• The main composer stays usable and shows Stop while the main session works.
• A failed subagent with no transcript shows a "Subagent session failed" error screen.
• A failed subagent with a transcript shows the error as a banner above its messages.

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A session.error event with a non-root sessionId now routes to a new onChildSessionError callback and returns before the shared root status or onError path. An event without a sessionId keeps the legacy root behavior. This keeps a child failure from touching the parent status indicator.

Files

• packages/cloud-agent-sdk/src/service-state.ts — adds onChildSessionError to ServiceStateConfig; processSessionError routes non-root sessionId events to it and returns before the root error path.
• packages/cloud-agent-sdk/src/session.ts — adds onChildSessionError to CloudAgentSessionConfig and forwards it to createServiceState.

The session manager records each child's failure message in a new childSessionErrorsAtom map and exposes a read-only childSessionError atom that returns the message for a child id, or null. The map clears with the other atoms on switch and destroy, so a stale child error cannot leak into the next session.

Files

• packages/cloud-agent-sdk/src/session-manager.ts — adds the childSessionError atom to SessionManagerAtoms, the backing map, the derived reader, the onChildSessionError handler, and the clear/reset wiring.

The child session sheet renders a runtime failure only in the failed child: a child with no messages shows a "Subagent session failed" error state, and a child with messages shows an error banner above the transcript. The parent detail screen reads the per-child error atom and passes the open child's message into the sheet.

Files

• apps/mobile/src/components/agents/child-session-sheet-state.ts — getChildSessionSheetState takes a sessionError argument and returns error for it when the child has no messages.
• apps/mobile/src/components/agents/child-session-sheet.tsx — accepts sessionError; renders the no-message error state or the above-transcript banner.
• apps/mobile/src/components/agents/session-detail-content.tsx — reads manager.atoms.childSessionError and passes the open child's message to the sheet.

Tests: 3 test files updated (child-session-sheet-state.test.ts, service-state.test.ts, session-manager.test.ts).
Generated: none.

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Verification

One iOS device round ran two cases.

Case	What it proves	Platform	Result
S1 — parent happy path	The parent session shows the Stop control while the agent works, then returns the composer to a usable state with no error text above it.	iOS	passed
S2 — cold-start reopen	Reopening the parent session shows a usable composer and no error text above it.	iOS	passed

No defect was reproduced on an unfixed build: the fix landed before round 1, so no round ran on an unfixed build.

Visual Changes

Parent session detail screen (mobile). The user sees a usable composer and no error banner above it after a message round trip. In the picture, the Preparation complete row sits above the Message... composer, where an error banner would appear, and no error text is present.

Reviewer Notes

Human steps: none needed.

Notes: none.

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Executive Summary

Incremental review of the server root-ID adoption fix; child-error routing now stays on the parent path after session.created, with high confidence.

Files Reviewed (2 files)

• packages/cloud-agent-sdk/src/service-state.ts
• packages/cloud-agent-sdk/src/service-state.test.ts

Previous Review Summary (commit 6e384af)

Current summary above is authoritative. Previous snapshots are kept for context only.

Previous review (commit 6e384af)

Status: No Issues Found | Recommendation: Merge

Files Reviewed (9 files)

• packages/cloud-agent-sdk/src/service-state.ts
• packages/cloud-agent-sdk/src/service-state.test.ts
• packages/cloud-agent-sdk/src/session.ts
• packages/cloud-agent-sdk/src/session-manager.ts
• packages/cloud-agent-sdk/src/session-manager.test.ts
• apps/mobile/src/components/agents/child-session-sheet-state.ts
• apps/mobile/src/components/agents/child-session-sheet-state.test.ts
• apps/mobile/src/components/agents/child-session-sheet.tsx
• apps/mobile/src/components/agents/session-detail-content.tsx

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_{Reviewed by grok-4.6 · Input: 144K · Output: 8.2K · Cached: 173.3K}

_{Review guidance: REVIEW.md from base branch main}

[pandemicsyn]

lgtm one in line