diff --git a/.debugging b/.debugging
index 6051974f4..01268e152 100644
--- a/.debugging
+++ b/.debugging
@@ -306,6 +306,25 @@ Expected: only interrupted `running` / `pending` call IDs are recovered, complet
   - Result: 7021 pass, 1 skip, 0 fail across 725 files.
   - Cleanup: validation worktree removed.
 
+## Cubic Follow-up
+
+- Latest Cubic review on PR #4106 initially reported: `1 issue found`, confidence `3/5`.
+- Cubic found a valid edge case in `src/hooks/session-recovery/recover-tool-result-missing.ts`: `callID ?? id` discarded recoverable `tool_use` parts when `callID` existed but was malformed and `id` was valid.
+- Red tests added:
+  - `recoverToolResultMissing > falls back to a valid id when callID is malformed`
+  - The interrupted idle recovery test now uses malformed `callID` plus valid `tool_use.id`.
+- Red output before the fix:
+  - `recoverToolResultMissing` returned `false` instead of `true`.
+  - `handleInterruptedToolResultsOnIdle` returned `false` instead of `true`.
+- Fix: choose a valid `callID` first, then fall back to a valid `id`; apply the same validity check in the idle precheck.
+- Post-fix validation:
+  - `bun test src/hooks/session-recovery/recover-tool-result-missing.test.ts --test-name-pattern "malformed"`: pass.
+  - `bun test src/hooks/session-recovery/hook.test.ts --test-name-pattern "interrupted idle recovery"`: pass.
+  - `bun test src/hooks/session-recovery/recover-tool-result-missing.test.ts src/hooks/session-recovery/hook.test.ts src/features/background-agent/task-completion-cleanup.test.ts src/plugin/event.test.ts --bail`: 53 pass, 0 fail.
+  - `bun --install=fallback /Users/yeongyu/.config/opencode/skills/typescript-programmer/scripts/check-no-excuse-rules.ts src/hooks/session-recovery/hook.ts src/hooks/session-recovery/hook.test.ts src/hooks/session-recovery/recover-tool-result-missing.ts src/hooks/session-recovery/recover-tool-result-missing.test.ts`: pass.
+  - `bun run typecheck`: pass.
+  - `bun run build`: pass.
+
 ## Final Status Before PR
 
 - Product behavior change: only malformed idle events with unfinished latest assistant messages and `pending` / `running` tool parts get synthetic interrupted tool results.
diff --git a/src/hooks/session-recovery/hook.test.ts b/src/hooks/session-recovery/hook.test.ts
index aa5fc9807..f1a2c8a5a 100644
--- a/src/hooks/session-recovery/hook.test.ts
+++ b/src/hooks/session-recovery/hook.test.ts
@@ -140,6 +140,7 @@ describe("session-recovery hook interrupted idle recovery", () => {
                   {
                     type: "tool_use",
                     id: "toolu_running",
+                    callID: "prt_not_a_tool_use_id",
                     name: "bash",
                     input: {},
                     state: { status: "running" },
@@ -147,6 +148,7 @@ describe("session-recovery hook interrupted idle recovery", () => {
                   {
                     type: "tool_use",
                     id: "toolu_pending",
+                    callID: "also_not_a_tool_use_id",
                     name: "task",
                     input: {},
                     state: { status: "pending" },
diff --git a/src/hooks/session-recovery/hook.ts b/src/hooks/session-recovery/hook.ts
index e64ea58ec..ca8f3f1d7 100644
--- a/src/hooks/session-recovery/hook.ts
+++ b/src/hooks/session-recovery/hook.ts
@@ -67,12 +67,21 @@ export function createSessionRecoveryHook(ctx: PluginInput, options?: SessionRec
     return typeof completed === "string" && completed.length > 0
   }
 
+  const partHasValidToolUseID = (part: NonNullable<MessageData["parts"]>[number]): boolean => {
+    const callID = part.callID
+    if (typeof callID === "string" && /^(toolu_|call_)/.test(callID)) {
+      return true
+    }
+
+    const id = part.id
+    return typeof id === "string" && /^(toolu_|call_)/.test(id)
+  }
+
   const messageHasInterruptedToolResults = (message: MessageData): boolean => {
     return message.parts?.some((part) =>
       (part.type === "tool" || part.type === "tool_use")
       && (part.state?.status === "pending" || part.state?.status === "running")
-      && typeof (part.callID ?? part.id) === "string"
-      && /^(toolu_|call_)/.test(part.callID ?? part.id ?? "")
+      && partHasValidToolUseID(part)
     ) === true
   }
 
diff --git a/src/hooks/session-recovery/recover-tool-result-missing.test.ts b/src/hooks/session-recovery/recover-tool-result-missing.test.ts
index 18a7755bf..442b9aad9 100644
--- a/src/hooks/session-recovery/recover-tool-result-missing.test.ts
+++ b/src/hooks/session-recovery/recover-tool-result-missing.test.ts
@@ -92,6 +92,35 @@ describe("recoverToolResultMissing", () => {
     })
   })
 
+  it("falls back to a valid id when callID is malformed", async () => {
+    //#given
+    const { client, promptAsync } = createMockClient()
+    const failedAssistantWithMalformedCallID: MessageData = {
+      info: { id: "msg_failed", role: "assistant" },
+      parts: [{
+        type: "tool_use",
+        id: "toolu_recovered_from_id",
+        callID: "prt_not_a_tool_use_id",
+        state: { status: "running" },
+      }],
+    }
+
+    //#when
+    const result = await recoverToolResultMissing(client, "ses_1", failedAssistantWithMalformedCallID, undefined, {
+      recoverStatuses: new Set(["pending", "running"]),
+    })
+
+    //#then
+    expect(result).toBe(true)
+    expect(promptAsync).toHaveBeenCalledTimes(1)
+    const call = promptAsync.mock.calls[0]?.[0] as {
+      body: {
+        parts: Array<{ toolUseId: string }>
+      }
+    }
+    expect(call.body.parts.map((part) => part.toolUseId)).toEqual(["toolu_recovered_from_id"])
+  })
+
   it("sends only interrupted sqlite tool results when recoverStatuses is provided", async () => {
     //#given
     sqliteBackend = true
diff --git a/src/hooks/session-recovery/recover-tool-result-missing.ts b/src/hooks/session-recovery/recover-tool-result-missing.ts
index 40e923b83..f7ae2af06 100644
--- a/src/hooks/session-recovery/recover-tool-result-missing.ts
+++ b/src/hooks/session-recovery/recover-tool-result-missing.ts
@@ -51,10 +51,20 @@ function isValidToolUseID(id: string | undefined): id is string {
   return typeof id === "string" && /^(toolu_|call_)/.test(id)
 }
 
+function selectValidToolUseID(part: { id?: string; callID?: string }): string | undefined {
+  if (isValidToolUseID(part.callID)) {
+    return part.callID
+  }
+  if (isValidToolUseID(part.id)) {
+    return part.id
+  }
+  return undefined
+}
+
 function normalizeMessagePart(part: { type: string; id?: string; callID?: string; state?: { status?: unknown } }): MessagePart | null {
   if (part.type === "tool" || part.type === "tool_use") {
-    const toolUseID = part.callID ?? part.id
-    if (!isValidToolUseID(toolUseID)) {
+    const toolUseID = selectValidToolUseID(part)
+    if (!toolUseID) {
       return null
     }