Regression: session startup/resume stuck at 'loading transcript' until a manual reload #283

Symptom

On app startup (rehydrate) and on continuing a killed session (resume), the pane is stuck at "loading transcript" indefinitely. Running a manual reload command clears it. Regression — worked before.

Root-cause investigation (so far)

The transcript-load lifecycle has an asymmetric state-write bug:

• `loadInitialHistoryForSession` (`src/renderer/src/workspace/hook/actions/initialHistory.ts`) sets `transcriptStatus: 'loading'` unconditionally (creating the runtime entry, ~line 118).
• But it only writes the terminal `'ready'` (~line 256) / `'error'` (~line 295) inside an `if (!current) return prev` guard (lines 144 and 290).

So if the session's runtime entry is rebuilt / dropped / renamed while the async load is in flight, the `'ready'` write is silently discarded and the pane stays at `'loading'` forever. A manual reload re-runs the load against a now-stable id, which is why it unsticks.

Why the manual reload path works but auto doesn't

`reloadAgentSessions` (the manual path) does its id-remap `setRuntimes` first, then calls the loader last under the stable new id. The auto paths interleave the loader with state rebuilds.

Prime suspect for the drop

`commitRehydratedState` (`src/renderer/src/workspace/hook/persistence/rehydrate.ts:374-`) is the only wholesale runtimes rebuild in the codebase — it returns a fresh `out = {}` map. Every other `setRuntimes` is additive `{...prev}`. A load-vs-rebuild ordering race here (or in the resume/`replaceSession` path) would orphan the in-flight loader's `'ready'` write.

Likely regression window: "Stream initial history loading" (`4765e51`, introduced the async slot/streaming load) and/or the #248 id-remap commits (`f85cfa5`/`ae42bd7`/`49472fb`).

Status

Every ordering traced on paper still preserves the id, so this is a genuine async race (or an unread path). Next step is diagnostic instrumentation (separate PR) that logs every `transcriptStatus` transition + flags when the loader resolve finds its runtime gone and when `commitRehydratedState` drops an in-flight `'loading'` key — reproduce once, read the timeline, then fix at the source.

Acceptance

• Startup and resume reach `transcriptStatus: 'ready'` automatically (no manual reload).
• No regression to live streaming / ghost reconciliation.