provider: stale composite reasoning item id (rs_A:rs_B) replayed after restart → invalid_request_error

Summary

After a service restart, the first reasoning turn of a resumed session fails on
a Responses-API provider with invalid_request_error: Referenced reasoning item 'rs_A:rs_B' was not found or has expired. Stored reasoning parts carry a
colon-composite itemId (responseRef:itemRef), which the backend accepts
while fresh but rejects once its server-side response state is gone. Every
subsequent fresh turn works; only the first post-restart resumed turn fails.

Environment

• opencode version: 0.0.0-beta-19271
• OS: Linux 6.17.0-1009-oracle (linux arm64)
• Terminal: Unavailable: headless service (systemd)
• Shell: /bin/bash
• Install/channel: beta
• Active plugins: oh-my-opencode-slim, conclave-v2 (local path),
  magic-context-v2 (local path). Note: a temporary redacted wire-logging
  plugin was attached during diagnosis and removed afterwards.

Reproduction

1. Start a reasoning session against a Responses-style provider that keeps
   server-side response state (observed via OpenCode Zen Go gateway).
2. Run several reasoning turns (succeeds; reasoning parts persist with
   metadata.openai.itemId shaped rs_<A>:rs_<B>).
3. Restart the opencode service.
4. Resume the same session with one more reasoning turn.
5. First post-restart turn fails with the error below; later turns recover.

Expected Behavior

Resume after restart either replays a reference the backend still resolves, or
falls back to self-contained reasoning content without failing the turn.

Actual Behavior

Error from provider (Console Go): Upstream request failed: [invalid_request_error] Referenced reasoning item 'rs_6aa28a10c05cf9f566f44022:rs_01a08aeb51217b92a5b853a0cb5b20ca' was not found or has expired.

Observed twice, both times as the first reasoning turn after a restart
(05:15→05:26 and 10:43→10:44 UTC); hundreds of same-format composite ids were
accepted intra-lifetime, so format alone is not the trigger — staleness across
restart/resume is.

Additional Context

• Stored part (redacted): {"type":"reasoning","text":"", "metadata":{"openai":{"itemId":"rs_<A>:rs_<B>", "reasoningEncryptedContent":"<present, long blob>"}}} — i.e. empty text,
  composite id, encrypted content present.
• Session types affected: long-lived resumed sessions; fresh sessions unaffected.
• Not caused by user plugins: Magic Context v2 only appends a text system
  block (source-verified, no reasoning handling); oh-my-opencode-slim contains
  zero references to previous_response_id/encrypted_content (source-verified).
• Frequency: intermittent — only first post-restart resumed reasoning turn.
• Workaround: resend the message (next turn self-heals).