Summary

When bulk-processing past emails (the "Process rules" / assistant history UI), threads were left entirely uncategorized when their first message was outside the selected date range (or just not processed).

Root cause: the UI dedupes to one representative message per thread — the most recent (ProcessRules.tsx). For a multi-message thread that representative is a mid-thread message (message.id !== message.threadId → isReplyInThread true). The matcher's thread-continuity guard in findPotentialMatchingRules then skips every runOnThreads=false categorization rule (Notification, Receipt, Marketing, …) because the thread has no prior category, leaving the model only the conversation meta-rule → no match → the whole thread gets no label.

Measured impact on a real bulk run: ~8% of processed emails (system notifications — deliveries, order updates, receipts) ended up with no category, all confirmed as threads with zero applied rule.

Fix

Add an isHistorical flag, set by the bulk UI, threaded
runRulesAction → runRules → findMatchingRules → findPotentialMatchingRules.
When set, the thread-continuity skip is bypassed so categorization runs on the representative message and the thread gets categorized.

// match-rules.ts
if (isThread && !isHistorical && !rule.runOnThreads) { /* skip */ }

Why this is safe

• Real-time unchanged (isHistorical defaults false): first message of a thread still categorizes; later messages still continue the existing category. No new real-time AI calls, no behaviour change.
• No double-labelling: the bulk path already dedupes to one message per thread, so there is no concurrent same-thread categorization that could assign competing labels.

Test plan (TDD)

• match-rules.test.ts (written first, watched fail, then green):
  • historical run + thread message + no prior category → categorization rule is offered (not in skippedThreadRuleNames);
  • real-time run, same setup → rule is skipped (continuity guard preserved).
• Full unit suite green (pnpm test): 0 failures.
• pnpm --filter inbox-zero-ai build:ci green (type-check across the threaded flag).

🤖 Generated with Claude Code