Keep Agent Mode session titles consistent across tabs and history - #3380

Relates to #3378

Why

A user can rename an Agent Mode tab, then open Recent Chats or the previous-sessions list and still see the first prompt instead. Saved chat notes kept the tab label and history title in different fields, so finding a named workflow meant reopening chats one by one.

What

Before: Rename a saved session in its tab; history can keep the original prompt title. Rename it in history; its reopened tab can keep the older label.

After: Both views show the latest user-assigned title, including after reopening the chat. Clearing a title restores the filename fallback.

Existing chats use their saved history title, then their saved tab label, then the filename. Native-only sessions continue to use their local session index.

Non goal

• Generate AI-written titles.
• Rename saved Markdown files or the coding agent's own session store.

Screenshot

No screenshot is attached because the dedicated dev vault displays unrelated note content beside Agent Chat. The live UI checks and saved-note inspection are recorded below.

Risk

High — this changes writes to saved chat notes and serializes a rename with an in-flight autosave. The existing frontmatter fields remain compatible with older chats, but a revert cannot undo a title the user changed while running this version.

Review: inspect AgentChatPersistenceManager.saveSession(), updateTopic(), and readExistingMeta() in src/agentMode/session/AgentChatPersistenceManager.ts, then AgentSessionManager.getChatHistoryItems(), updateChatTitle(), readSessionRefFromFile(), and renameSession() in src/agentMode/session/AgentSessionManager.ts. Run Verification steps 1–4, including the clear-title and overlapping-save cases.

Verification

1. In a disposable Obsidian vault, create an Agent Mode chat, send a prompt, rename its tab, and confirm Recent Chats and Chat History show the new name without opening the chat.
2. Save that chat as a Markdown note, rename it from history, reopen it, and confirm the tab uses the new name. Rename the tab again and confirm the list follows. Restart Obsidian and check both names again.
3. Repeat with chat autosave off and a configured hidden conversations folder. Clear a saved title and confirm history falls back to its filename instead of the old name.
4. Rename a saved chat while it is autosaving, then reopen it; the most recent user name should remain. Check an older chat with no saved label still has its prior fallback title.

Observed in Obsidian before the review fixes (logan-dev-vault): The built plugin was loaded and its new title code was confirmed at runtime. Renaming an existing Claude session tab changed Chat History and Recent Chats; opening it from Recent Chats kept the title. On a saved Markdown chat, a later tab rename updated the note’s agentLabel and Recent Chats. The saved title remained after disabling and re-enabling the plugin. I restored the test chat’s original title afterward. One immediate rename during the first manual save exposed a race; a deterministic red/green regression test now covers the reconciliation. The other edge cases in steps 3–4 are covered by unit tests, not a live UI run. Obsidian reported no captured errors.

Review-fix verification (6d33d60): Four focused suites pass (251 tests), including folded YAML reopening, BOM/CRLF compatibility, hidden-folder history titles, transcript preservation, and the filename fallback after clearing saved title fields. The new regression cases were observed failing before the corrections. Format, lint, production build, and the Obsidian review gate pass. These review fixes were verified with unit tests, without another live Obsidian UI run.