`session_store_sql` silently returns empty when session sync is set to local

[bscheurm]

Describe the bug

When sessionSync.level = "local" (user chose "Keep on this device only"), the session_store_sql tool is still injected into every agent's system message and remains callable — but returns 0 rows for all tables. There is no indication to agents that the cloud store is empty because sync is disabled — agents can't distinguish this from a user who genuinely has no session history.

The local ~/.copilot/session-store.db has all the data (600+ sessions, 5,000+ turns), but the system message directs agents to use session_store_sql for session history queries, so they conclude there's no history.

Steps to reproduce

1. Select "Keep on this device only" when prompted for session storage (config: sessionSync: [{ origin: "*", level: "local" }])
2. Use the CLI — sessions accumulate in ~/.copilot/session-store.db
3. In any session, ask "what did I work on this week?" or have an agent query session_store_sql
4. Agent gets 0 results and reports no session history

Expected behavior

When cloud sync is disabled, one of:

1. Don't expose session_store_sql — if the cloud store won't have data, don't offer the tool
2. Have session_store_sql query the local DB — the schemas are compatible (sessions, turns, checkpoints, session_files, session_refs exist in both)
3. At minimum, annotate the tool description so agents know the cloud store won't have data when sync is disabled, and can fall back to the local DB

The above are suggestions — the team likely has better ideas for the right approach given the broader session storage architecture.

Actual behavior

• session_store_sql is injected unconditionally with no awareness of the sessionSync config
• Returns 0 rows for all queries — agents can't distinguish "no sessions" from "sync disabled"
• The system message actively encourages agents to use this tool for temporal queries ("what did I work on?", "find prior sessions", etc.)

Impact

• Automated agents (maintenance tasks, briefings, session digests) that query session_store_sql silently get wrong results
• The /chronicle feature and any built-in session history features are effectively broken for local-only users
• No error or warning — just empty results that look like valid "no data" responses

Environment

• Copilot CLI: 1.0.24
• OS: Windows 11
• Config: sessionSync: [{ origin: "*", level: "local" }]
• Local session-store.db: 105 MB, 613 sessions, 5,342 turns (healthy)
• Cloud session store: 0 rows across all tables

Workaround

Query ~/.copilot/session-store.db directly via Python/sqlite3. The schema is compatible. This requires every consumer of session data to implement fallback logic.