Sub-agent child tool-call arguments are not persisted in turn-state snapshots, so reloaded child tool cards lose their input

[YellowSnnowmann]

Summary

After a reload, a sub-agent's child tool-call cards render without their input: the turn-state snapshot never persists the child call's arguments, so the frontend mapper has nothing to restore.

Problem

Live, subagent_tool_call carries args and the row shows the tool input (and a degraded generic tool name can be given a search label from query). After a thread reload the same cards come back from the persisted snapshot with no input at all.

Neither persisted shape carries the payload (app/src/types/turnState.ts):

export interface PersistedSubagentToolCall {
  callId; toolName; status; iteration?; elapsedMs?; outputChars?;
  displayName?; detail?; failure?; output?;      // no args / input
}
// PersistedSubagentTranscriptItem, kind: 'tool'
{ iteration?; callId; toolName; status; elapsedMs?; outputChars?; displayName?; detail?; failure? }

The only args field in that file is PersistedToolTimelineEntry.argsBuffer, which belongs to the parent timeline. So subagentToolCallFromPersisted assigning no args (app/src/store/chatRuntimeSlice.ts, subagentActivityFromPersisted) is not a mapper bug — the data never leaves the core.

Repro: delegate to a sub-agent that calls a tool with visible arguments → let it finish → reload the thread → expand the sub-agent card → the child tool row has no input.

Solution

Rust: persist the child call's arguments in the turn-state mirror (src/openhuman/threads/turn_state/ — where subagent_tool_call events are written into the snapshot's subagent.toolCalls), as an optional field mirroring the parent's argsBuffer semantics (bounded size). Frontend: add the optional field to PersistedSubagentToolCall / the transcript tool item and copy it through in subagentToolCallFromPersisted — a one-line change once the field exists.

Acceptance criteria

• Repro gone — child tool rows keep their input across a reload; a degraded tool name still derives its search label from the restored query.
• Regression safety — Rust snapshot round-trip test covers the new field; Vitest covers subagentActivityFromPersisted restoring args.
• Diff coverage ≥ 80% — the fix PR meets the changed-lines coverage gate (Vitest + cargo-llvm-cov, enforced by .github/workflows/ci-lite.yml).
• Older snapshots without the field still load (additive, optional).

Related

• Raised in review on fix(chat): preserve and render complete agent turns #5885 (CodeRabbit, chatRuntimeSlice.ts — "Restore persisted child tool arguments"); confirmed there as a core-side gap outside that PR's scope.