Controller ignores ExecRequest.last_seq: disconnected clients cannot replay missed events

[joycel-github]

Summary

The ax exec --last-seq <n> flag is accepted by the CLI and sent on the wire, but the controller never reads ExecRequest.LastSeq. A disconnected client that reconnects with --last-seq does not get the events it missed replayed; the field is silently ignored.

Evidence

• Client sets it: cmd/ax/exec.go (--last-seq flag → ExecRequest.LastSeq).
• Proto field exists: proto/ax.proto (int32 last_seq = 3;).
• No server-side reader: LastSeq / GetLastSeq() has zero non-test references anywhere under internal/ (including internal/controller/). Controller.Exec resumes purely from conversation state via ResumptionState, never filtering/replaying by sequence.

Regression

Server-side last_seq handling used to exist:

• Dashboard conversation history collapses when scrolling #202 renamed last_seen_seq → last_seq
• ConversationEvent.harness_config should be bytes #262 "return error when requested last_seq is missing from event log" filtered events (ev.Seq > req.LastSeq) in tryResuming

The recent controller rewrite in #308 ("Handle default harness correctly") replaced tryResuming/ResumptionState, and the last_seq handling was dropped in the process.

Impact

• Disconnect/reconnect replay is broken: a client that saw up to seq N and reconnects with --last-seq N still cannot backfill the events it missed while a conversation was in flight.
• The flag is effectively dead: it is documented and accepted but has no effect.

Repro

1. Start a conversation and note the last seq printed.
2. Disconnect the client mid-execution.
3. Reconnect: ax exec --conversation <id> --last-seq <n> --resume.
4. Observe the missed events between <n> and the current head are not replayed.

Expected

Either:

• Restore server-side last_seq handling so the controller replays events with seq > last_seq (as in ConversationEvent.harness_config should be bytes #262), returning a clear error when last_seq is not in the event log; or
• If the field is intentionally deprecated, remove it from the CLI/proto and update docs.

Notes

Docs corrected in #319 (README no longer promises the replay behavior) while this code gap is open. Related historical discussion: #7 (closed).