fix(acp): recover chat history after reconnect

[athanzxyt]

Description

Restore authoritative ACP chat history when live turn updates are missed during a disconnect.

• refresh history after an accepted prompt settles and whenever Host availability returns
• give optimistic submissions unique sequence IDs and reconcile them against distinct user turns in submission order
• preserve consecutive identical prompts until each prompt's authoritative turn exists

The change stays in the renderer projection layer; it does not alter the ACP protocol, runtime state machine, provider processes, or dependencies.

Related issues

Complements #3062, which makes transient SSH/Wire disconnects publish the Host recovery edge used here.

Testing

• focused ACP browser suite (26 tests)
• focused ACP store and live-session node tests (7 tests)
• pnpm --filter @emdash/emdash-desktop format:check
• pnpm --filter @emdash/emdash-desktop lint
• pnpm --filter @emdash/emdash-desktop typecheck
• full desktop suite: 3,617 tests passed and 1 skipped. Two unrelated browser tests failed: the untouched workspace-settings-section.browser.test.tsx fixture omits workspaceOptions, and an agent-selector hover test timed out under suite load but passed immediately in isolation (2 tests).

Screenshot/Recording (if applicable)

Not applicable; this restores transcript state without changing layout or styling.

Checklist

• I kept this PR small and focused
• I ran a self-review before opening this PR
• I ran the relevant local checks or explained why not
• I updated docs when behavior or setup changed
• I added or updated tests when behavior changed, or explained why not
• I only added comments where the logic is not obvious
• I used Conventional Commits for the commit message and PR title

[greptile-apps]

Greptile Summary

The PR refreshes authoritative ACP history after accepted prompts and Host recovery, then reconciles optimistic prompts against newer committed user turns.

• Adds a submission-sequence baseline to avoid matching identical prompts from older history.
• Requests history refreshes after prompt acceptance and Host recovery.
• Adds browser tests for disconnect recovery, repeated prompt text, and Host availability transitions.
• Updates ACP runtime architecture documentation.

Confidence Score: 4/5

The repeated-submission reconciliation defect should be fixed before merging because one accepted prompt can remove a later identical optimistic prompt.

The new sequence-and-text predicate does not identify a specific submission, so rapid consecutive prompts with the same text can cause the first committed turn to clear the second prompt's optimistic state.

Files Needing Attention: apps/emdash-desktop/src/core/features/conversations/browser/acp/acp-chat-store.ts; apps/emdash-desktop/src/renderer/tests/browser/acp-chat-store-submission.test.ts

Important Files Changed

Filename	Overview
apps/emdash-desktop/src/core/features/conversations/browser/acp/acp-chat-store.ts	Adds recovery refreshes and baseline-based optimistic reconciliation, but equal consecutive submissions can be associated with the wrong committed turn.
apps/emdash-desktop/src/renderer/tests/browser/acp-chat-store-submission.test.ts	Covers stale identical history and reconnect recovery but omits consecutive identical submissions sharing the same baseline.
agents/architecture/acp-runtime.md	Documents the new renderer-side authoritative-history refresh behavior.

Sequence Diagram

sequenceDiagram
  participant User
  participant Store as ACP chat store
  participant Host as ACP Host
  participant History as Authoritative history

  User->>Store: Submit prompt
  Store->>Store: Record baseline and optimistic prompt
  Store->>Host: sendPrompt()
  Host-->>Store: Accepted
  Store->>History: Refresh history
  History-->>Store: Committed turns
  Store->>Store: Match newer user turn and reconcile
  Host-->>Store: Host ready after reconnect
  Store->>History: Refresh missed committed turns

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Prompt To Fix All With AI

### Issue 1
apps/emdash-desktop/src/core/features/conversations/browser/acp/acp-chat-store.ts:866-875
**Text matching clears wrong prompt**

When identical text is submitted twice before the first submission publishes its working state, the first committed turn satisfies this shared baseline-and-text predicate and clears the second optimistic prompt before its authoritative turn exists, causing the later submission to disappear temporarily from the transcript and message count.

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For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.

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