The test 'falls back to most recent session when no to is provided' was
using resolveStorePath() which returns the real ~/.warelay/sessions.json.
This overwrote production session data with test values, causing session
fragmentation issues.
Changed to use a temp directory like other tests.
Bug fixes:
- Empty result field handling: Changed truthy check to explicit type
check (`typeof parsed?.text === "string"`) in command-reply.ts.
Previously, Claude CLI returning `result: ""` would cause raw JSON
to be sent to WhatsApp.
- Response prefix on heartbeat: Apply `responsePrefix` to heartbeat
alert messages in runReplyHeartbeat, matching behavior of regular
message handler.
