[davidrobertson]

File-history retrieval could report no history for recently changed files when the session store contained partial legacy rows. Missing start times made the date comparator return NaN before the handler selected its 15 sessions, and null rows could crash retrieval.

Reuse the existing validated session selector in the shared file-context handler. Keep the current project filter, current-session exclusion, and 15-session limit. Add regressions for null/partial rows and filtering before the limit.

Validation:

• Reproduced three failures before the fix; all four regression cases now pass.
• Build, skill generation/checks, and docs synchronization passed.
• Full suite: 2,687 passed, four skipped.
• TypeScript reports the same pre-existing diagnostics as unchanged main, with byte-identical baseline and candidate logs.
• Applied the candidate build to the local daemon after backing up the original runtime. The same native MCP file-history query changed from no history to five stored observations, including the upgrade's restart-handling change.

The patch does not migrate or delete stored data. Local verification artifacts are under /private/tmp/agentmemory-file-history-evidence.