Phase 13 — Conversation Session Navigator

Adds a ConversationsWindow that lists all past sessions with title and age, and lets the user rejoin any session — loading its full message history back into Gemma's context window. A new session starts fresh as today; rejoin continues from where the conversation left off.

What Already Exists

ConversationService persists sessions to .conversation_history.json on every append_messages
Rejoining is mechanically trivial — MainWindow._session_id is just a UUID; setting it to an old session ID makes _build_messages load that session's history automatically
MemoryWindow Context tab already shows the message array for a session — confirms the data is there

What Needs Building

Session metadata: started_at, last_active, title — not currently stored
list_sessions() method on ConversationService
ConversationsWindow — floating panel showing sessions table
Rejoin wiring: MainWindow.rejoin_session(session_id)
Sidebar button to open the window
Tile slot in the layout grid

Design Decisions

Floating ConversationsWindow, not a sidebar expansion. Consistent with existing MemoryWindow / CriticWindow / DocumentsWindow pattern. Gets its own tile slot (col 2, row 1 — currently empty in the grid). Can be opened from a new sidebar button.

Session title = first 60 chars of first user message. Auto-derived; no manual naming needed. Stored in session metadata so it doesn't require re-scanning messages on every list refresh.

Rejoin clears the conversation log but keeps the session. The log widget is visual-only — clearing it doesn't affect ConversationService. A "── rejoined session ──" marker is appended so the user knows the context is loaded.

Schema migration on load. Current file format is {session_id: [messages]}. New format: {session_id: {messages: [...], started_at: float, last_active: float, title: str}}. Old format detected on load (value is a list) and auto-migrated: title derived from first message, timestamps set to current time. No manual migration step.

UI Layout

conversations Refresh ──────────────────────────────────────────────────────── Title Msgs Age ──────────────────────────────────────────────────────── ● here is the URL that gives an outl… 24 13h 🔁 🗑 how about client-server architectu… 8 9m 🔁 🗑 what is Alexander the Great known … 4 49s 🔁 🗑 ──────────────────────────────────────────────────────── ● = current session 🔁 = rejoin 🗑 = delete

Current session highlighted (●). Clicking 🔁 on any row rejoins that session. Clicking 🗑 deletes the session (with confirmation). Sessions ordered newest first by last_active.

Implementation Plan

13a · ConversationService

Schema migration + session metadata

Change	Detail
New storage format	`{session_id: {messages, started_at, last_active, title}}`
Migration on load	Detect list value → wrap, derive title from first user message, timestamps = now
append_messages()	Update `last_active` on every write; set `started_at` + `title` on first write
list_sessions()	Returns `[{session_id, title, message_count, started_at, last_active}]` sorted by `last_active` desc
delete_session(session_id)	Remove from dict and save
get_history() unchanged	Still returns messages list — no callers need to change

The schema change is internal to ConversationService. All callers use get_history() and append_messages() which keep the same signatures. Tests use :memory: sentinel so no disk interaction.

13b · ConversationsWindow

Floating session list panel

Table: Title | Msgs | Age | Actions (🔁 rejoin, 🗑 delete)
Current session row marked with ● bullet and highlighted
Sessions ordered newest first; refreshed on showEvent and Refresh button
Delete: QMessageBox confirmation, then conv.delete_session() + refresh
Rejoin: calls self._rejoin_callback(session_id) — callback injected by MainWindow at construction
Constructor: ConversationsWindow(conversation_service, session_id_getter, rejoin_callback)

13c · MainWindow wiring

Rejoin, sidebar button, tile slot

Change	Detail
rejoin_session(session_id)	Sets `self._session_id`, clears log widget, appends "── rejoined ──" marker, raises ConversationsWindow to refresh
ConversationsWindow construction	Created at startup alongside MemoryWindow; injected with `shared_conv`, session_id_getter, and `self.rejoin_session` callback
Sidebar button	💬 icon; opens/raises ConversationsWindow
Tile slot	col 2, row 1 (currently empty) in `_tile_windows()`
New session (⟳) button	Already exists; no change needed — it sets a new UUID which naturally creates a new session on next `append_messages`

Files Changed

File	Change
src/local/services/conversation_service.py	Schema migration, metadata fields, list_sessions(), delete_session()
src/local/ui/conversations_window.py	New file — sessions table, rejoin/delete actions
src/local/ui/main_window.py	Construct ConversationsWindow, rejoin_session(), sidebar button, tile slot
tests/test_conversation_service.py	Tests for list_sessions, delete_session, schema migration

Out of Scope

Session renaming — title is auto-derived for now; can add later
Compaction — addressed in a future phase; rejoining a long session still hits the 40-message cap (raising the cap is a quick config change, separate from this)
Engram-as-pointer architecture — the current ConversationService-as-source-of-truth is retained; the pointer design is a future refactor once session navigation is proven out
num_ctx increase — quick config change, can be done independently