diff --git a/.changeset/FN-5985-mission-goal-not-found-contract.md b/.changeset/FN-5985-mission-goal-not-found-contract.md
new file mode 100644
index 0000000000..929b9e2e62
--- /dev/null
+++ b/.changeset/FN-5985-mission-goal-not-found-contract.md
@@ -0,0 +1,5 @@
+---
+"@runfusion/fusion": patch
+---
+
+Fix mission→goal link write paths to return `400 { code: "GOAL_NOT_FOUND" }` instead of 404 for unknown goals, aligning the API, CLI, and pi tool contract.
diff --git a/docs/missions.md b/docs/missions.md
index 055ea02413..dc998519db 100644
--- a/docs/missions.md
+++ b/docs/missions.md
@@ -146,7 +146,7 @@ Fusion surfaces the persisted mission↔goal linkage through REST, CLI, and pi-e
 | `POST /api/missions/:missionId/goals/:goalId` | Idempotently link one goal to a mission. |
 | `DELETE /api/missions/:missionId/goals/:goalId` | Idempotently unlink one goal from a mission. |
 
-The mission detail payload keeps `linkedGoals` separate from the milestone tree so read paths can surface strategy context without traversing slices/features. All goal-link write endpoints preserve the same invariant: missing goals return `404`, archived goals reject with `400 { code: "GOAL_ARCHIVED" }`, duplicate/relinked ids are no-ops, and unlink remains allowed even after a goal is archived.
+The mission detail payload keeps `linkedGoals` separate from the milestone tree so read paths can surface strategy context without traversing slices/features. All goal-link write endpoints preserve the same invariant: missing goals on link write paths (`POST /api/missions`, `PATCH /api/missions/:missionId`, `PUT /api/missions/:missionId/goals`, `POST /api/missions/:missionId/goals/:goalId`) reject with `400 { code: "GOAL_NOT_FOUND" }`, archived goals reject with `400 { code: "GOAL_ARCHIVED" }`, duplicate/relinked ids are no-ops, and the `DELETE /api/missions/:missionId/goals/:goalId` unlink path treats unknown goals as a `404` while remaining allowed even after a goal is archived.
 
 ### CLI
 
diff --git a/packages/dashboard/src/__tests__/mission-goal-links-routes.test.ts b/packages/dashboard/src/__tests__/mission-goal-links-routes.test.ts
index a703236ed4..583e0bc378 100644
--- a/packages/dashboard/src/__tests__/mission-goal-links-routes.test.ts
+++ b/packages/dashboard/src/__tests__/mission-goal-links-routes.test.ts
@@ -104,7 +104,10 @@ describe("mission goal linkage routes", () => {
       { "content-type": "application/json" },
     );
 
-    expect(missingResponse.status).toBe(404);
+    expect(missingResponse.status).toBe(400);
+    expect(missingResponse.body).toMatchObject({
+      details: { code: "GOAL_NOT_FOUND", goalId: "G-404" },
+    });
   });
 
   it("replaces linked goals via patch, clears with [], and ignores undefined goalIds", async () => {
@@ -176,7 +179,10 @@ describe("mission goal linkage routes", () => {
       JSON.stringify({ goalIds: [goalB.id, "G-404"] }),
       { "content-type": "application/json" },
     );
-    expect(missingResponse.status).toBe(404);
+    expect(missingResponse.status).toBe(400);
+    expect(missingResponse.body).toMatchObject({
+      details: { code: "GOAL_NOT_FOUND", goalId: "G-404" },
+    });
     expect(store.getMissionStore().listGoalIdsForMission(mission.id)).toEqual([goalA.id]);
   });
 
@@ -221,7 +227,10 @@ describe("mission goal linkage routes", () => {
       JSON.stringify({ goalIds: [goalA.id, "G-404"] }),
       { "content-type": "application/json" },
     );
-    expect(missingResponse.status).toBe(404);
+    expect(missingResponse.status).toBe(400);
+    expect(missingResponse.body).toMatchObject({
+      details: { code: "GOAL_NOT_FOUND", goalId: "G-404" },
+    });
     expect(store.getMissionStore().listGoalIdsForMission(mission.id)).toEqual([goalB.id, goalC.id]);
   });
 
@@ -247,7 +256,10 @@ describe("mission goal linkage routes", () => {
     expect(store.getMissionStore().listGoalIdsForMission(mission.id)).toEqual([goal.id]);
 
     const missingResponse = await request(app, "POST", `/api/missions/${mission.id}/goals/G-404`);
-    expect(missingResponse.status).toBe(404);
+    expect(missingResponse.status).toBe(400);
+    expect(missingResponse.body).toMatchObject({
+      details: { code: "GOAL_NOT_FOUND", goalId: "G-404" },
+    });
   });
 
   it("removes a linked archived goal idempotently", async () => {
@@ -305,7 +317,7 @@ describe("mission goal linkage routes", () => {
     expect(deleteBad.status).toBe(400);
   });
 
-  it("returns 404 for missing mission or goal", async () => {
+  it("returns 404 for missing missions and unlinking unknown goals", async () => {
     const mission = store.getMissionStore().createMission({ title: "Ship mission" });
     const goal = store.getGoalStore().createGoal({ title: "Goal A" });
 
@@ -325,7 +337,10 @@ describe("mission goal linkage routes", () => {
     expect(missingMissionPatch.status).toBe(404);
 
     const missingGoalAdd = await request(app, "POST", `/api/missions/${mission.id}/goals/G-404`);
-    expect(missingGoalAdd.status).toBe(404);
+    expect(missingGoalAdd.status).toBe(400);
+    expect(missingGoalAdd.body).toMatchObject({
+      details: { code: "GOAL_NOT_FOUND", goalId: "G-404" },
+    });
 
     const missingGoalSet = await request(
       app,
@@ -334,7 +349,10 @@ describe("mission goal linkage routes", () => {
       JSON.stringify({ goalIds: [goal.id, "G-404"] }),
       { "content-type": "application/json" },
     );
-    expect(missingGoalSet.status).toBe(404);
+    expect(missingGoalSet.status).toBe(400);
+    expect(missingGoalSet.body).toMatchObject({
+      details: { code: "GOAL_NOT_FOUND", goalId: "G-404" },
+    });
 
     const missingGoalDelete = await request(app, "DELETE", `/api/missions/${mission.id}/goals/G-404`);
     expect(missingGoalDelete.status).toBe(404);
diff --git a/packages/dashboard/src/mission-routes.ts b/packages/dashboard/src/mission-routes.ts
index 72e836440a..e424e5f487 100644
--- a/packages/dashboard/src/mission-routes.ts
+++ b/packages/dashboard/src/mission-routes.ts
@@ -332,7 +332,14 @@ export function createMissionRouter(
   }
 
   function requireLinkableGoal(goalId: string): Goal {
-    const goal = requireGoal(goalId);
+    if (!validateGoalId(goalId)) {
+      throw badRequest("Invalid goal ID format");
+    }
+
+    const goal = getScopedGoalStore().getGoal(goalId);
+    if (!goal) {
+      throw badRequest("Goal not found", { code: "GOAL_NOT_FOUND", goalId });
+    }
     if (goal.status === "archived") {
       throw badRequest("Cannot link an archived goal", { code: "GOAL_ARCHIVED", goalId });
     }