fix(client): cold replay child session + project migration recompute edge cases (#315)

* fix(client): cold replay child session + project migration recompute edge cases

Bug 1: child sessions created during cold activation lacked _cold flag,
hitting the hot recompute path per-entry (O(n²)). Gate on _coldActivating.

Bug 2: post-activation only recomputed the activated session's project.
Now recomputes child sessions and all projects (covers cwd migration).

Fixes #314

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix(client): use replay-seen sids instead of parentSessionId for cold child recompute

parentSessionId is null on mergeColdSessions-created entries, so the
previous parentSessionId === id check missed them entirely. Collect
session IDs from replay entries directly, clear _cold on all of them.

Fixes #314

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix(client): try/finally for _coldActivating + re-render child session cards

Codex review P2 fixes:
- Wrap replay loop in try/finally so _coldActivating resets even if
  addEntry throws (prevents permanent suppression of live recompute).
- Re-render child session cards after recompute so their displayed
  counts/costs reflect the corrected stats, not the seeded doubles.

Fixes #314

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix(client): zero child session stats before cold replay to prevent displayNum inflation

mergeColdSessions seeds child sessions with count/cost from the session
index. Without zeroing before replay, addEntry increments on top of the
seeded values — displayNum starts at N+1 instead of 1, and final counts
double. Zero on first encounter in the replay loop, same as the parent.

Fixes #314

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* refactor(client): extract zeroSessionStats to eliminate triplicated stat-field list

Code review finding: the 10-field stat zeroing block was duplicated at
parent and child zero sites. Adding a stat field would require edits at
3 places (shotgun surgery risk). Single helper, called from both.

Fixes #314

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* refactor(client): use zeroSessionStats in recomputeSessionStats too

Round-2 code review caught the 4th inline copy of the 10-field stat
zeroing in recomputeSessionStats. Same helper, single source of truth.

Fixes #314

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Justin Lee <justinlee@91app.com>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: 3 people

public/entry-rendering.js

@@ -635,7 +635,7 @@ function addEntry(e) {
   // Live (hot): full recompute from allEntries (idempotent, O(n) per entry).
   // Batch: increment counts for displayNum; defer full recompute to post-batch.
   // Cold: increment all stats (entries not in allEntries; full recompute on activation).
-  if (!_loading && !sess._cold) {
+  if (!_loading && !sess._cold && !window._coldActivating) {
     recomputeSessionStats(sid);
     recomputeProjectCost(projName);
     if (prevProjectName && prevProjectName !== projName) recomputeProjectCost(prevProjectName);
@@ -919,9 +919,7 @@ function addEntry(e) {
 function recomputeSessionStats(sid) {
   const sess = sessionsMap.get(sid);
   if (!sess) return;
-  sess.count = 0; sess.mainCount = 0; sess.subCount = 0; sess.retryCount = 0;
-  sess.totalCost = 0; sess.inputTokens = 0; sess.outputTokens = 0;
-  sess.toolCalls = {}; sess.toolCallTurns = 0; sess.toolFailTurns = 0;
+  zeroSessionStats(sess);
   for (var i = 0; i < allEntries.length; i++) {
     var en = allEntries[i];
     if (en.sessionId !== sid) continue;

public/miller-columns.js

@@ -2166,6 +2166,12 @@ function formatCurrentStepBreadcrumb() {
   return 'step #' + (step.stepIdx + 1) + subLabel;
 }
 
+function zeroSessionStats(s) {
+  s.count = 0; s.mainCount = 0; s.subCount = 0; s.retryCount = 0;
+  s.totalCost = 0; s.inputTokens = 0; s.outputTokens = 0;
+  s.toolCalls = {}; s.toolCallTurns = 0; s.toolFailTurns = 0;
+}
+
 function selectSession(id) {
   setFocus('sessions');
   if (id === selectedSessionId) return;
@@ -2208,23 +2214,49 @@ function selectSession(id) {
         // #308: zero stats before replay — sessions.json seeded them; addEntry
         // increments on top (cold path), so without zeroing = double-count.
         // Replay with _cold still true → incremental counts, not O(n²) recompute.
-        sess.count = 0; sess.mainCount = 0; sess.subCount = 0; sess.retryCount = 0;
-        sess.totalCost = 0; sess.inputTokens = 0; sess.outputTokens = 0;
-        sess.toolCalls = {}; sess.toolCallTurns = 0; sess.toolFailTurns = 0;
+        zeroSessionStats(sess);
         const entries = data.entries || [];
+        // Track all sessions touched during replay (child sessions, migrations)
+        const replaySids = new Set([id]);
         window._coldActivating = true;
-        for (const e of entries) addEntry(e);
-        window._coldActivating = false;
-        sess._cold = false;
-        if (typeof recomputeSessionStats === 'function') recomputeSessionStats(id);
-        const projName = getProjectName(sess.cwd);
-        if (typeof recomputeProjectCost === 'function') recomputeProjectCost(projName);
+        try {
+          for (const e of entries) {
+            if (e.sessionId && !replaySids.has(e.sessionId)) {
+              replaySids.add(e.sessionId);
+              // Zero child session stats seeded by mergeColdSessions (same reason as parent)
+              const cs = sessionsMap.get(e.sessionId);
+              if (cs && cs._cold) zeroSessionStats(cs);
+            }
+            addEntry(e);
+          }
+        } finally {
+          window._coldActivating = false;
+        }
+        // Clear _cold for all replayed sessions (parent + children)
+        for (const sid of replaySids) {
+          const s = sessionsMap.get(sid);
+          if (s) s._cold = false;
+        }
+        if (typeof recomputeSessionStats === 'function') {
+          for (const sid of replaySids) recomputeSessionStats(sid);
+        }
+        // Recompute all projects — cwd migration means old project needs update too
+        if (typeof recomputeProjectCost === 'function') {
+          for (const [name] of projectsMap) recomputeProjectCost(name);
+        }
         if (data.sessionTitles) {
           for (const [sid, title] of Object.entries(data.sessionTitles)) {
             const s = sessionsMap.get(sid);
             if (s && !s.title) s.title = title;
           }
         }
+        // Re-render child session cards to reflect recomputed stats
+        for (const sid of replaySids) {
+          if (sid === id) continue;
+          const childEl = document.getElementById('sess-' + sid.slice(0, 8));
+          const childSess = sessionsMap.get(sid);
+          if (childEl && childSess) childEl.innerHTML = renderSessionItem(childSess, sid, childEl);
+        }
         // Render — use _renderSelectedSession to avoid selectSession's id===selected guard
         if (spinner.parentNode) spinner.remove();
         _renderSelectedSession(id);