IssueSyncer #formatTimelineEvent crashes on null assignee/label/subIssue/parent/etc (defensive null-safety needed)

Context

Operator ran npm run ai:sync-github-workflow from main checkout post-#11470 merge. After progressing through 8506 issues (created chunks up to v8.1.0/chunk-40), sync crashed with:

❌ Sync failed: TypeError: Cannot read properties of null (reading 'login')
    at #formatTimelineEvent (ai/services/github-workflow/sync/IssueSyncer.mjs:202:58)
    at #formatIssueMarkdown (IssueSyncer.mjs:171:50)
    at IssueSyncer.pullFromGitHub (IssueSyncer.mjs:522:48)

Problem

IssueSyncer.mjs:202 reads event.assignee.login directly with an inline comment: // Assuming assignee is always a User. That assumption fails when the user has been deleted on GitHub — the timeline event's assignee field comes back as null from the GraphQL API, and .login throws.

The same null-deref pattern exists across the entire #formatTimelineEvent switch:

Note line 186 already null-safes event.actor and event.author (event.actor?.login || event.author?.login || 'Ghost'). The pattern was known but coverage is incomplete.

Each unhandled null aborts the entire sync_all run — wasting all the GraphQL cost spent (~516 cost units in this trace).

Architectural Reality

#formatTimelineEvent formats GitHub GraphQL timelineItems.nodes entries into Markdown timeline lines. GitHub may return null for any referenced entity that has been:

• Deleted (user, label, sub-issue, parent, blocking-issue)
• Force-pushed away (commits)
• Cross-referenced from a now-deleted issue/PR

The function runs per-event for thousands of issues during clean-slate sync. ONE null entity ANYWHERE in ANY issue's timeline crashes the whole sync.

The Fix

Add uniform null-safety to #formatTimelineEvent switch cases using optional chaining + fallback markers:

case 'AssignedEvent':
    details = `assigned to @${event.assignee?.login || 'Ghost'}`;
    break;
case 'UnassignedEvent':
    details = `unassigned from @${event.assignee?.login || 'Ghost'}`;
    break;
case 'LabeledEvent':
    details = `added the \`${event.label?.name || '(deleted label)'}\` label`;
    break;
// ... etc. for all switch cases that deref fields

Fallback markers ('Ghost' for users matches existing event.actor?.login || event.author?.login || 'Ghost' pattern at line 186; '(deleted X)' or '?' for other entities).

Acceptance Criteria

• All switch cases in #formatTimelineEvent use optional chaining (?.) when dereferencing any nested field that GitHub can return as null (assignee, label, subIssue, parent, blockingIssue, blockedIssue, commit, source).
• Each null-deref site has a meaningful fallback marker that preserves Timeline section readability (e.g., 'Ghost' for users matches existing convention; '(deleted label)', '(deleted)' for other entities; '?' for numbers).
• Unit test verifies #formatTimelineEvent produces a graceful string output (no exception, no 'undefined'/'null' artifacts in output) for at least: AssignedEvent-with-null-assignee, LabeledEvent-with-null-label, SubIssueAddedEvent-with-null-subIssue. Other null paths covered by inspection.
• No regression in normal-path Timeline rendering (existing test of #formatTimelineEvent on populated events continues to pass).
• sync_all can run to completion past this crash point without aborting on null-entity events (post-merge validation).

Out of Scope

• Log-volume reduction during sync (separate concern — operator surfaced "very intense" per-issue log line volume; deserves its own enhancement ticket).
• Skipping/filtering nullable timeline events entirely (defensive null-safety preserves the event surface in markdown for archive integrity; filtering loses information).
• Adding GraphQL-side null-filter on the query (returns less data; same architectural concern).
• Migrating #formatTimelineEvent to a more declarative renderer pattern (out-of-scope refactor).

Avoided Traps

• Filtering null events at fetch time: loses information in archived issue Timeline sections; deleted-user/deleted-label history is valuable archive context even when the entity is gone.
• Returning early on null: same loss as filtering.
• Wrapping each case in try/catch: works but obscures the systematic pattern; uniform optional-chaining is the architecturally cleaner expression.
• Only fixing AssignedEvent (the empirical crash): whack-a-mole — next sync_all run hits a null subIssue or label and crashes again. Defensive coverage is the right scope.

Related

• Parent context: post-merge of #11470 (ADR 0004 Phase 1 close-out CLI enabler) — operator's first attempt to run the full clean-slate sync surfaced this bug.
• Authority artifact: GitHub GraphQL API spec — timelineItems entities may have null fields when referenced entities are deleted.
• Adjacent: log-volume enhancement (separate ticket TBD per operator's 2026-05-16 observation).

Origin Session ID: 0064efde-455e-4ecd-a26f-574381b3766a

Retrieval Hint: query_raw_memories(query="IssueSyncer formatTimelineEvent null assignee login deleted user timeline event GraphQL")