Fix Codex transcript convergence

PLAN.md

@@ -113,6 +113,10 @@ seq N", so there is no separate history path to drift from the live one.
 - `UserMessage { text }` — echoed into the transcript **by the manager, not
   by drivers**, so every device renders the conversation from one stream.
 - `AssistantText { delta }` — streaming text, rendered as markdown.
+- `AssistantTextFinal { text }` — the provider's authoritative value for the
+  open assistant message. It replaces its preceding provisional deltas while
+  remaining an append-only transcript event, so live SSE, replay and paging
+  converge on the same words.
 - `ToolStart / ToolUpdate / ToolEnd { tool, input, output }`.
   The tool vocabulary is common too (2026-09-09), not just the envelope:
   Codex's `/usr/bin/bash -lc` argv and Claude's Bash call are both
@@ -247,13 +251,13 @@ remains the turn's usage. If an older common transcript has no such event yet,
 the server seeds the same measurement from the last `token_count` in Codex's
 own rollout, including when that rollout is on an SSH setup.
 
-App-server assistant text comes only from its durable
-`item/agentMessage/delta` notifications; the full text on `item/completed` is
-always the consolidated copy and is ignored. This is decided from the dialect,
-not an in-memory set of ids: after a backend restart, the previous deltas can
-be behind the persisted stdout cursor while the completion is still ahead,
-and forgetting which ids streamed used to append the complete message after
-its already-recorded prefix.
+App-server's `item/agentMessage/delta` notifications are provisional: safety
+buffering can revise their words before `item/completed` supplies the durable
+text. The driver records that completion as `AssistantTextFinal`; the phone
+replaces the open message both live and on replay. A distinct append-only event
+also makes adoption safe: if a backend restart falls between the deltas and the
+completion, the correction is still meaningful without process-local memory
+of which item ids streamed.
 
 ### The llama driver