diff --git a/packages/agentctx/src/extract/run.ts b/packages/agentctx/src/extract/run.ts
index 32d8faf..49b38d5 100644
--- a/packages/agentctx/src/extract/run.ts
+++ b/packages/agentctx/src/extract/run.ts
@@ -120,13 +120,13 @@ async function extract(
 
   const db = openDatabase(env.dbPath);
   try {
-    recordCost(db, sessionId, totalCost);
+    const projectId = sessionProjectId(db, sessionId) ?? resolveProjectId(env.cwd);
+    recordCost(db, sessionId, projectId, totalCost);
     const result = parseExtraction(responseText);
     if (result === null) {
       log(`extract: unparseable model output for session ${sessionId} — skipped`);
       return 0;
     }
-    const projectId = sessionProjectId(db, sessionId) ?? resolveProjectId(env.cwd);
     const stats = ingestExtraction(db, projectId, sessionId, result, log);
     logStats(log, sessionId, stats, totalCost, result.flushOk);
   } finally {
@@ -135,13 +135,27 @@ async function extract(
   return 0;
 }
 
-/** Self-accounting (SPEC §3.1, §7): cost lands on the session row. */
-function recordCost(db: ReturnType<typeof openDatabase>, sessionId: string, cost: number): void {
+/**
+ * Self-accounting (SPEC §3.1, §7): cost lands on the session row, attributed to
+ * its project. When the cost row is the session's first DB write (a sparse
+ * session that never triggered a SessionStart/UserPromptSubmit injection),
+ * `project_id` would otherwise stay NULL and `status` would drop the cost from
+ * the per-project total. Fill it here, but never clobber a value an injection
+ * already set.
+ */
+function recordCost(
+  db: ReturnType<typeof openDatabase>,
+  sessionId: string,
+  projectId: string,
+  cost: number,
+): void {
   db.prepare(
-    `INSERT INTO sessions (session_id, extraction_cost_usd) VALUES (@sessionId, @cost)
+    `INSERT INTO sessions (session_id, project_id, extraction_cost_usd)
+       VALUES (@sessionId, @projectId, @cost)
      ON CONFLICT(session_id) DO UPDATE SET
-       extraction_cost_usd = extraction_cost_usd + @cost`,
-  ).run({ sessionId, cost });
+       extraction_cost_usd = extraction_cost_usd + @cost,
+       project_id = COALESCE(project_id, @projectId)`,
+  ).run({ sessionId, projectId, cost });
 }
 
 function sessionProjectId(db: ReturnType<typeof openDatabase>, sessionId: string): string | null {
diff --git a/packages/agentctx/test/extract/run.test.ts b/packages/agentctx/test/extract/run.test.ts
index c4c0e36..c7efa04 100644
--- a/packages/agentctx/test/extract/run.test.ts
+++ b/packages/agentctx/test/extract/run.test.ts
@@ -104,6 +104,24 @@ describe("agentctx extract", () => {
     }
   });
 
+  it("attributes the cost to the project even with no prior injection", async () => {
+    // Sparse session: the cost row is the first DB write (no SessionStart /
+    // UserPromptSubmit injection ever ran), so project_id must be filled here
+    // or `status` drops the cost from the per-project total (#66).
+    const calls: MockCall[] = [];
+    expect(await run({ fetchFn: mockFetch(calls), apiKey: "key" })).toBe(0);
+
+    const db = openDatabase(t.env.dbPath);
+    try {
+      const session = db
+        .prepare("SELECT project_id FROM sessions WHERE session_id = 's1'")
+        .get() as { project_id: string | null };
+      expect(session.project_id).toBe(resolveProjectId(t.env.cwd));
+    } finally {
+      db.close();
+    }
+  });
+
   it("degrades cleanly without an API key (SPEC §8 rung 3)", async () => {
     const calls: MockCall[] = [];
     expect(await run({ fetchFn: mockFetch(calls), apiKey: undefined })).toBe(0);