fix(scheduler): use mightWrite for dependency chain and topological sort

When a lift function returns undefined on first run, no write is recorded
in the journal. This broke the dependency chain in pull mode because:
1. updateDependents only looked at actual writes
2. topologicalSort only used actual writes for ordering

Fix: Initialize mightWrite from declared writes during subscribe, and use
mightWrite (instead of just log.writes) in both updateDependents and
topologicalSort.

Adds test case that reproduces the nested lift scenario where inner lift
initially returns undefined.

Fixes counter-when-unless-operators test which has nested lifts where
the inner lift initially returns undefined.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: seefeldb

packages/runner/src/scheduler.ts

@@ -690,6 +690,13 @@ export class Scheduler {
     const reads = sortAndCompactPaths(log.reads);
     const writes = sortAndCompactPaths(log.writes);
     this.dependencies.set(action, { reads, writes });
+
+    // Initialize mightWrite with declared writes from subscribe
+    // This ensures dependency chain can be built even before action runs
+    if (writes.length > 0) {
+      this.updateMightWrite(action, { reads, writes });
+    }
+
     return reads;
   }
 
@@ -723,8 +730,12 @@ export class Scheduler {
           const otherLog = this.dependencies.get(otherAction);
           if (!otherLog) continue;
 
+          // Use mightWrite if available (accumulates all paths action has ever written)
+          // This ensures dependency chain is built even if first run writes undefined
+          const otherWrites = this.mightWrite.get(otherAction) ?? otherLog.writes;
+
           // Check if otherAction writes to this entity we're reading
-          for (const write of otherLog.writes) {
+          for (const write of otherWrites) {
             if (
               read.space === write.space &&
               read.id === write.id &&
@@ -1059,6 +1070,7 @@ export class Scheduler {
       const sorted = topologicalSort(
         new Set(dirtyMembers),
         this.dependencies,
+        this.mightWrite,
         this.actionParent,
       );
 
@@ -1141,6 +1153,7 @@ export class Scheduler {
     const sorted = topologicalSort(
       new Set(dirtyMembers),
       this.dependencies,
+      this.mightWrite,
       this.actionParent,
     );
 
@@ -1662,6 +1675,7 @@ export class Scheduler {
     const order = topologicalSort(
       workSet,
       this.dependencies,
+      this.mightWrite,
       this.actionParent,
     );
 
@@ -1753,6 +1767,7 @@ export class Scheduler {
 function topologicalSort(
   actions: Set<Action>,
   dependencies: WeakMap<Action, ReactivityLog>,
+  mightWrite: WeakMap<Action, IMemorySpaceAddress[]>,
   actionParent?: WeakMap<Action, Action>,
 ): Action[] {
   const graph = new Map<Action, Set<Action>>();
@@ -1768,7 +1783,8 @@ function topologicalSort(
   for (const actionA of actions) {
     const log = dependencies.get(actionA);
     if (!log) continue;
-    const { writes } = log;
+    // Use mightWrite if available (includes declared writes even if first run writes undefined)
+    const writes = mightWrite.get(actionA) ?? log.writes;
     const graphA = graph.get(actionA)!;
     for (const write of writes) {
       for (const actionB of actions) {

packages/runner/test/scheduler.test.ts

@@ -4357,3 +4357,161 @@ describe("parent-child action ordering", () => {
     expect(childRunCount).toBe(0);
   });
 });
+
+describe("pull mode with references", () => {
+  let storageManager: ReturnType<typeof StorageManager.emulate>;
+  let runtime: Runtime;
+  let tx: IExtendedStorageTransaction;
+
+  beforeEach(() => {
+    storageManager = StorageManager.emulate({ as: signer });
+    runtime = new Runtime({
+      apiUrl: new URL(import.meta.url),
+      storageManager,
+    });
+    runtime.scheduler.enablePullMode();
+    tx = runtime.edit();
+  });
+
+  afterEach(async () => {
+    await tx.commit();
+    await runtime?.dispose();
+    await storageManager?.close();
+  });
+
+  it("should propagate dirtiness through references (nested lift scenario)", async () => {
+    // This test reproduces the nested lift pattern where:
+    // - Inner lift reads source, writes to innerOutput
+    // - outerInput cell contains a REFERENCE to innerOutput
+    // - Outer lift reads outerInput (following ref to innerOutput), writes to outerOutput
+    // - Effect reads outerOutput
+    //
+    // When source changes:
+    // 1. Inner lift is marked dirty
+    // 2. Outer lift should be marked dirty because it reads (via reference) what inner writes
+    // 3. Effect should run and see updated value
+
+    const source = runtime.getCell<string[]>(
+      space,
+      "nested-ref-source",
+      undefined,
+      tx,
+    );
+    source.set([]);
+
+    const innerOutput = runtime.getCell<string | undefined>(
+      space,
+      "nested-ref-inner-output",
+      undefined,
+      tx,
+    );
+    innerOutput.set(undefined);
+
+    // This cell holds a REFERENCE to innerOutput (simulating how lift passes results)
+    const outerInput = runtime.getCell<string | undefined>(
+      space,
+      "nested-ref-outer-input",
+      undefined,
+      tx,
+    );
+    // Set it to be a reference pointing to innerOutput
+    outerInput.set(undefined);
+
+    const outerOutput = runtime.getCell<string>(
+      space,
+      "nested-ref-outer-output",
+      undefined,
+      tx,
+    );
+    outerOutput.set("default");
+
+    const effectResult = runtime.getCell<string>(
+      space,
+      "nested-ref-effect-result",
+      undefined,
+      tx,
+    );
+    effectResult.set("");
+
+    await tx.commit();
+    tx = runtime.edit();
+
+    let innerRuns = 0;
+    let outerRuns = 0;
+    let effectRuns = 0;
+
+    // Inner lift: arr => arr[0] (returns undefined when array is empty)
+    const innerLift: Action = (actionTx) => {
+      innerRuns++;
+      const arr = source.withTx(actionTx).get() ?? [];
+      const firstItem = arr[0]; // Returns undefined when empty!
+      innerOutput.withTx(actionTx).send(firstItem);
+    };
+
+    // Outer lift: (name, firstItem) => name || firstItem || "default"
+    // For this test, we'll read innerOutput directly to simulate following the reference
+    const outerLift: Action = (actionTx) => {
+      outerRuns++;
+      const firstItem = innerOutput.withTx(actionTx).get();
+      const result = firstItem || "default";
+      outerOutput.withTx(actionTx).send(result);
+    };
+
+    // Effect: sink that captures the output
+    const effect: Action = (actionTx) => {
+      effectRuns++;
+      const val = outerOutput.withTx(actionTx).get();
+      effectResult.withTx(actionTx).send(val ?? "");
+    };
+
+    // Subscribe in order: inner, outer, effect
+    runtime.scheduler.subscribe(
+      innerLift,
+      {
+        reads: [source.getAsNormalizedFullLink()],
+        writes: [innerOutput.getAsNormalizedFullLink()],
+      },
+      { scheduleImmediately: true },
+    );
+    await runtime.idle();
+
+    runtime.scheduler.subscribe(
+      outerLift,
+      {
+        reads: [innerOutput.getAsNormalizedFullLink()],
+        writes: [outerOutput.getAsNormalizedFullLink()],
+      },
+      { scheduleImmediately: true },
+    );
+    await runtime.idle();
+
+    runtime.scheduler.subscribe(
+      effect,
+      {
+        reads: [outerOutput.getAsNormalizedFullLink()],
+        writes: [effectResult.getAsNormalizedFullLink()],
+      },
+      { scheduleImmediately: true, isEffect: true },
+    );
+    await runtime.idle();
+
+    // Initial state: source is [], innerOutput is undefined, outerOutput is "default"
+    expect(innerRuns).toBe(1);
+    expect(outerRuns).toBe(1);
+    expect(effectRuns).toBe(1);
+    expect(effectResult.get()).toBe("default");
+
+    // Now change source to ["apple"]
+    source.withTx(tx).send(["apple"]);
+    await tx.commit();
+    tx = runtime.edit();
+    await runtime.idle();
+
+    // With fix: All should run because dependency chain is now properly built
+    // (mightWrite preserves declared writes, enabling correct topological ordering)
+    expect(innerRuns).toBe(2);
+    expect(outerRuns).toBe(2);
+    expect(effectRuns).toBe(2);
+    expect(effectResult.get()).toBe("apple");
+  });
+});