Memoize derived thread reads

[juliusmarminge]

Summary

• Memoize derived thread reads so repeated selectors can reuse stable thread objects when underlying state is unchanged.
• Extract shared thread derivation logic into threadDerivation.ts to reduce duplication between store selectors and store updates.
• Add coverage for selector stability, cache invalidation, and thread existence checks.
• Simplify the chat thread route to use the new existence selector and avoid an extra effect for diff-open tracking.

Testing

• Added apps/web/src/store.test.ts coverage for memoized thread derivation and existence checks.
• Not run: bun fmt
• Not run: bun lint
• Not run: bun typecheck
• Not run: bun run test

---

Note

Medium Risk
Introduces new WeakMap-based memoization for derived Thread objects and refactors selectors/store updates to use it, which could subtly affect referential equality and UI update behavior. Route-level diff panel mounting logic also changes state tracking per-thread, so regressions would mainly show up as stale/incorrect renders rather than data corruption.

Overview
Memoizes derived thread reads by centralizing thread derivation in getThreadFromEnvironmentState (new threadDerivation.ts) and caching derived Thread objects/collected arrays to keep references stable when underlying environment state is unchanged.

Updates store.ts and storeSelectors.ts to use the shared derivation helper, adds a lightweight selectThreadExistsByRef for existence checks without materializing threads, and adds tests in store.test.ts covering stability, invalidation, and existence.

Tweaks the chat thread route/diff UX: tracks “diff panel has opened” per thread key, passes onDiffPanelOpen into ChatView, and triggers it when opening/toggling diffs so diff content can stay mounted after first open.

^{Reviewed by Cursor Bugbot for commit 081d29b. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Memoize derived thread reads to avoid redundant recomputation

• Introduces getThreadFromEnvironmentState in threadDerivation.ts, which uses a WeakMap keyed on the thread shell to cache the fully composed Thread object, returning the same reference when inputs are unchanged.
• Adds a memoized collectByIds helper that caches derived arrays for messages, activities, proposed plans, and turn diff summaries using WeakMaps.
• Refactors createScopedThreadSelector in storeSelectors.ts to track EnvironmentState and threadId instead of individual per-thread slices, delegating derivation to getThreadFromEnvironmentState.
• Adds selectThreadExistsByRef selector in store.ts to check thread existence without materializing the full derived thread.
• Updates the chat thread route to track per-thread diff panel open state via an onDiffPanelOpen callback on ChatView, avoiding unnecessary re-renders tied to diffOpen.

^{Macroscope summarized 081d29b.}

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[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

Autofix Details

Bugbot Autofix prepared a fix for the issue found in the latest run.

• ✅ Fixed: Removed effect breaks diff content persistence after close
  • Restored a useEffect that watches diffOpen and sets hasOpenedDiff(true) whenever the diff becomes open, ensuring the DiffPanel stays mounted after close regardless of how the diff was opened.

Or push these changes by commenting:

@cursor push f0ed1ba77a

Preview (f0ed1ba77a)

diff --git a/apps/web/src/routes/_chat.$environmentId.$threadId.tsx b/apps/web/src/routes/_chat.$environmentId.$threadId.tsx
--- a/apps/web/src/routes/_chat.$environmentId.$threadId.tsx
+++ b/apps/web/src/routes/_chat.$environmentId.$threadId.tsx
@@ -204,11 +204,15 @@
       search: { diff: undefined },
     });
   }, [navigate, threadRef]);
+  useEffect(() => {
+    if (diffOpen) {
+      setHasOpenedDiff(true);
+    }
+  }, [diffOpen]);
   const openDiff = useCallback(() => {
     if (!threadRef) {
       return;
     }
-    setHasOpenedDiff(true);
     void navigate({
       to: "/$environmentId/$threadId",
       params: buildThreadRouteParams(threadRef),

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[macroscopeapp]

Approvability

Verdict: Approved

This is a performance optimization refactor that centralizes thread derivation logic into a new module with WeakMap-based memoization. The changes are well-tested, functionally equivalent to existing behavior, and don't introduce new features or runtime behavior changes.

^{You can customize Macroscope's approvability policy. Learn more.}

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

Bugbot Autofix prepared a fix for the issue found in the latest run.

• ✅ Fixed: Four exported functions are never imported externally
  • Removed the export keyword from selectThreadMessages, selectThreadActivities, selectThreadProposedPlans, and selectThreadTurnDiffSummaries since they are only used internally within threadDerivation.ts.

Or push these changes by commenting:

@cursor push 9176389c68

Preview (9176389c68)

diff --git a/apps/web/src/threadDerivation.ts b/apps/web/src/threadDerivation.ts
--- a/apps/web/src/threadDerivation.ts
+++ b/apps/web/src/threadDerivation.ts
@@ -60,10 +60,7 @@
   return nextValues;
 }
 
-export function selectThreadMessages(
-  state: EnvironmentState,
-  threadId: ThreadId,
-): Thread["messages"] {
+function selectThreadMessages(state: EnvironmentState, threadId: ThreadId): Thread["messages"] {
   return collectByIds(
     state.messageIdsByThreadId[threadId],
     state.messageByThreadId[threadId] ?? EMPTY_MESSAGE_MAP,
@@ -71,10 +68,7 @@
   );
 }
 
-export function selectThreadActivities(
-  state: EnvironmentState,
-  threadId: ThreadId,
-): Thread["activities"] {
+function selectThreadActivities(state: EnvironmentState, threadId: ThreadId): Thread["activities"] {
   return collectByIds(
     state.activityIdsByThreadId[threadId],
     state.activityByThreadId[threadId] ?? EMPTY_ACTIVITY_MAP,
@@ -82,7 +76,7 @@
   );
 }
 
-export function selectThreadProposedPlans(
+function selectThreadProposedPlans(
   state: EnvironmentState,
   threadId: ThreadId,
 ): Thread["proposedPlans"] {
@@ -93,7 +87,7 @@
   );
 }
 
-export function selectThreadTurnDiffSummaries(
+function selectThreadTurnDiffSummaries(
   state: EnvironmentState,
   threadId: ThreadId,
 ): Thread["turnDiffSummaries"] {

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^{Reviewed by Cursor Bugbot for commit 594dd8f. Configure here.}

[juliusmarminge]

@cursor push 9176389