feat: allow ticket implementation cancellation

crates/workspace-server/src/server.rs

@@ -1827,6 +1827,10 @@ pub fn build_router(api: WorkspaceApi) -> Router {
             "/api/w/{workspace_id}/tickets/{id}/assignments/{role}",
             put(scoped_set_ticket_assignment).delete(scoped_clear_ticket_assignment),
         )
+        .route(
+            "/api/w/{workspace_id}/tickets/{id}/implementation-cancellations",
+            post(scoped_cancel_ticket_implementation),
+        )
         .route(
             "/api/w/{workspace_id}/tickets/{id}/state",
             post(scoped_transition_ticket_state),
@@ -3176,6 +3180,14 @@ struct SetTicketRoleAssignmentRequest {
     expected_assignment_id: Option<String>,
 }
 
+#[derive(Debug, Deserialize)]
+#[serde(deny_unknown_fields)]
+struct CancelTicketImplementationRequest {
+    operation_id: String,
+    assignment_id: String,
+    reason: String,
+}
+
 #[derive(Debug, Default, Deserialize)]
 #[serde(deny_unknown_fields)]
 struct ClearTicketRoleAssignmentQuery {
@@ -3373,6 +3385,113 @@ async fn scoped_clear_ticket_assignment(
         assignment: None,
     }))
 }
+
+async fn scoped_cancel_ticket_implementation(
+    State(api): State<WorkspaceApi>,
+    AxumPath(path): AxumPath<ScopedRecordPath>,
+    Json(request): Json<CancelTicketImplementationRequest>,
+) -> ApiResult<Json<TicketDetail>> {
+    validate_workspace_scope(&api, &path.workspace_id)?;
+    let ticket = api.authority.ticket(&path.id)?;
+    let operation_id = require_ticket_assignment_value("operation_id", request.operation_id)?;
+    let assignment_id = require_ticket_assignment_value("assignment_id", request.assignment_id)?;
+    let reason = require_ticket_assignment_value("reason", request.reason)?;
+    if reason.len() > 512 {
+        return Err(Error::InvalidInput(
+            "implementation cancellation reason must be at most 512 bytes".to_string(),
+        )
+        .into());
+    }
+
+    if !matches!(
+        ticket.state.as_str(),
+        state if state == TicketWorkflowState::InProgress.as_str()
+            || state == TicketWorkflowState::Ready.as_str()
+    ) {
+        return Err(Error::TicketAssignmentConflict(format!(
+            "implementation cancellation requires an inprogress Ticket; current state is {}",
+            ticket.state
+        ))
+        .into());
+    }
+
+    let current = api.store.get_current_ticket_role_assignment(
+        &path.workspace_id,
+        &ticket.id,
+        TicketAssignmentRole::Coder,
+    )?;
+    if let Some(assignment) = current.filter(|value| value.assignment_id == assignment_id)
+        && let TicketAssignmentPrincipal::Worker {
+            runtime_id,
+            worker_id,
+        } = assignment.principal
+    {
+        if api
+            .store
+            .get_ticket_assignment_operation(&path.workspace_id, &operation_id)?
+            .is_some()
+        {
+            return Err(Error::TicketAssignmentConflict(format!(
+                "operation `{operation_id}` was already used for another Ticket assignment mutation"
+            ))
+            .into());
+        }
+        let worker = RuntimeWorkerRef::new(runtime_id, worker_id);
+        cancel_ticket_coder_worker(&api, &worker, &reason).await?;
+    }
+
+    let cancelled = api.store.cancel_current_ticket_coder_assignment(
+        &path.workspace_id,
+        &ticket.id,
+        &assignment_id,
+        &new_id("tasev"),
+        &new_id("tev"),
+        &operation_id,
+        "workspace-web",
+        &Utc::now().to_rfc3339_opts(SecondsFormat::Secs, true),
+        &reason,
+    )?;
+    if !cancelled {
+        return Err(Error::TicketAssignmentConflict(format!(
+            "assignment `{assignment_id}` is not the current Coder implementation"
+        ))
+        .into());
+    }
+    browser_ticket_detail(&api, &ticket.id)
+}
+
+async fn cancel_ticket_coder_worker(
+    api: &WorkspaceApi,
+    worker: &RuntimeWorkerRef,
+    reason: &str,
+) -> ApiResult<()> {
+    let session_lock = current_worker_session_lock(api, worker);
+    let _session_guard = session_lock.lock().await;
+    match api.runtime.cancel_worker(
+        worker,
+        WorkerLifecycleRequest {
+            reason: Some(format!("Ticket implementation cancelled: {reason}")),
+            ticket_assignment: None,
+        },
+    ) {
+        Ok(result) if result.state == WorkerOperationState::Accepted => {}
+        Ok(result) => {
+            return Err(ApiError::with_diagnostics(
+                Error::RuntimeOperationFailed {
+                    runtime_id: worker.runtime_id.clone(),
+                    code: "workspace_ticket_implementation_cancel_rejected".to_string(),
+                    message: "Runtime did not cancel the assigned Coder Worker".to_string(),
+                },
+                result.diagnostics,
+            ));
+        }
+        Err(RuntimeRegistryError::UnknownWorker { .. }) => {}
+        Err(error) => return Err(error.into_error().into()),
+    }
+    close_current_worker_session_locked(api, worker).await?;
+    Ok(())
+}
+
 fn validate_ticket_assignment_state(
     api: &WorkspaceApi,
     assignment: &WorkerTicketAssignmentRequest,
@@ -16015,6 +16134,114 @@ mod tests {
         assert_eq!(replayed_clear.assignment, None);
     }
 
+    #[tokio::test]
+    async fn implementation_cancellation_cancels_coder_and_returns_ticket_to_ready() {
+        let dir = tempfile::tempdir().unwrap();
+        let api = test_api(dir.path()).await;
+        let worker = api
+            .runtime
+            .spawn_worker(
+                EMBEDDED_WORKER_RUNTIME_ID,
+                test_create_binding(),
+                WorkerSpawnRequest {
+                    requested_worker_name: Some("cancelled-coder".to_string()),
+                    intent: WorkerSpawnIntent::TicketRole {
+                        ticket_id: "implementation-cancellation".to_string(),
+                        role: TicketWorkerRole::Coder,
+                    },
+                    acceptance: WorkerSpawnAcceptanceRequirement::RunAccepted {
+                        expected_segments: 0,
+                    },
+                    profile: ProfileSelector::Builtin("builtin:coder".to_string()),
+                    ticket_assignment: None,
+                    initial_submit: Vec::new(),
+                    working_directory_request: None,
+                    resolved_working_directory_request: None,
+                    resolved_working_directory: None,
+                    resolved_config_bundle: None,
+                    resolved_worker_observation_enabled: false,
+                    resolved_worker_observation_grants: Vec::new(),
+                    resolved_workspace_api: Some(test_worker_workspace_api(
+                        EMBEDDED_WORKER_RUNTIME_ID,
+                    )),
+                    resolved_memory_settings: Some(test_worker_memory_settings()),
+                    resolved_control_operation: None,
+                },
+            )
+            .unwrap()
+            .worker
+            .unwrap()
+            .worker;
+        let worker = RuntimeWorkerRef::new(EMBEDDED_WORKER_RUNTIME_ID, worker.worker_id);
+        api.store
+            .upsert_worker_registry(&WorkerRegistryRecord {
+                workspace_id: TEST_WORKSPACE_ID.to_string(),
+                worker: worker.clone(),
+                display_name: "Cancelled Coder".to_string(),
+                profile: Some("builtin:coder".to_string()),
+                retention_state: "normal".to_string(),
+                transcript_ref: None,
+                session_ref: None,
+                summary_ref: None,
+                diagnostics_ref: None,
+                created_at: TEST_CREATED_AT.to_string(),
+                updated_at: TEST_CREATED_AT.to_string(),
+            })
+            .unwrap();
+        let backend = browser_ticket_backend(&api).unwrap();
+        let mut input = ticket::NewTicket::new("Implementation cancellation");
+        input.workflow_state = Some(TicketWorkflowState::InProgress);
+        let ticket = backend.create(input).unwrap();
+        api.store
+            .set_current_ticket_coder_assignment(
+                &TicketCoderAssignmentRecord {
+                    workspace_id: TEST_WORKSPACE_ID.to_string(),
+                    ticket_id: ticket.id.clone(),
+                    assignment_id: "cancelled-assignment".to_string(),
+                    worker: worker.clone(),
+                    assigned_by: "test-user".to_string(),
+                    assigned_at: TEST_CREATED_AT.to_string(),
+                },
+                None,
+                "cancelled-assignment-event",
+                "cancelled-assignment-operation",
+                false,
+            )
+            .unwrap();
+        let path = || {
+            AxumPath(ScopedRecordPath {
+                workspace_id: TEST_WORKSPACE_ID.to_string(),
+                id: ticket.id.clone(),
+            })
+        };
+        let request = || {
+            Json(CancelTicketImplementationRequest {
+                operation_id: "cancel-implementation-operation".to_string(),
+                assignment_id: "cancelled-assignment".to_string(),
+                reason: "redo with the corrected design".to_string(),
+            })
+        };
+
+        let Json(cancelled) =
+            scoped_cancel_ticket_implementation(State(api.clone()), path(), request())
+                .await
+                .unwrap();
+        assert_eq!(cancelled.state, TicketWorkflowState::Ready.as_str());
+        assert!(cancelled.current_coder.is_none());
+        assert!(
+            !cancelled
+                .assignments
+                .iter()
+                .any(|assignment| assignment.role == "coder")
+        );
+        assert_eq!(api.runtime.worker(&worker).unwrap().state, "cancelled");
+
+        let Json(replayed) = scoped_cancel_ticket_implementation(State(api), path(), request())
+            .await
+            .unwrap();
+        assert_eq!(replayed.state, TicketWorkflowState::Ready.as_str());
+    }
+
     #[tokio::test]
     async fn authenticated_worker_ticket_mutation_notifies_current_assignment() {
         let dir = tempfile::tempdir().unwrap();

crates/workspace-server/src/store.rs

@@ -1086,6 +1086,18 @@ pub trait ControlPlaneStore: Send + Sync {
         occurred_at: &str,
         reason: Option<&str>,
     ) -> Result<bool>;
+    fn cancel_current_ticket_coder_assignment(
+        &self,
+        workspace_id: &str,
+        ticket_id: &str,
+        assignment_id: &str,
+        assignment_event_id: &str,
+        state_event_id: &str,
+        operation_id: &str,
+        actor: &str,
+        occurred_at: &str,
+        reason: &str,
+    ) -> Result<bool>;
     fn get_current_ticket_coder_assignment(
         &self,
         workspace_id: &str,
@@ -4084,106 +4096,110 @@ impl ControlPlaneStore for SqliteWorkspaceStore {
     ) -> Result<bool> {
         self.with_conn_mut(|conn| {
             let tx = conn.transaction_with_behavior(TransactionBehavior::Immediate)?;
-        let current = read_ticket_role_assignment_by_id(&tx, workspace_id, assignment_id)?;
+            let cleared = clear_current_ticket_role_assignment_in_tx(
-        let Some(current) = current.filter(|value| {
+                &tx,
-            value.ticket_id == ticket_id && value.role == role
-        }) else {
-            return Ok(false);
-        };
-        let principal_json = serde_json::to_string(&current.principal)
-            .map_err(|error| Error::Store(format!("serialize Ticket assignment principal: {error}")))?;
-        let mut hasher = Sha256::new();
-        for value in [
-            "ticket-role-assignment:clear:v1",
                 workspace_id,
                 ticket_id,
-            role.as_str(),
+                role,
                 assignment_id,
-            principal_json.as_str(),
+                event_id,
-            actor,
-            reason.unwrap_or(""),
-        ] {
-            hasher.update(value.as_bytes());
-            hasher.update([0]);
-        }
-        let fingerprint = hasher
-            .finalize()
-            .iter()
-            .map(|byte| format!("{byte:02x}"))
-            .collect::<String>();
-        let (principal_id, runtime_id, worker_id) = match &current.principal {
-            TicketAssignmentPrincipal::User { account_id } => {
-                (Some(account_id.as_str()), None, None)
-            }
-            TicketAssignmentPrincipal::Worker {
-                runtime_id,
-                worker_id,
-            } => (None, Some(runtime_id.as_str()), Some(worker_id.as_str())),
-            TicketAssignmentPrincipal::WorkspaceAgent { agent_key } => {
-                (Some(agent_key.as_str()), None, None)
-            }
-        };
-        let inserted = tx.execute(
-            "INSERT OR IGNORE INTO ticket_assignment_operations (
-                 workspace_id, operation_id, action, ticket_id, role, principal_kind,
-                 principal_id, runtime_id, worker_id, assignment_id,
-                 expected_assignment_id, created_at, request_fingerprint
-             ) VALUES (?1, ?2, 'unassign', ?3, ?4, ?5, ?6, ?7, ?8, ?9, ?9, ?10, ?11)",
-            params![
-                workspace_id,
                 operation_id,
-                ticket_id,
+                actor,
-                role.as_str(),
-                current.principal.kind(),
-                principal_id,
-                runtime_id,
-                worker_id,
-                assignment_id,
                 occurred_at,
-                fingerprint,
+                reason,
-            ],
+                "ticket-role-assignment:clear:v1",
             )?;
-        if inserted == 0 {
+            tx.commit()?;
-            let persisted: String = tx.query_row(
+            Ok(cleared)
-                "SELECT request_fingerprint FROM ticket_assignment_operations
+        })
-                  WHERE workspace_id = ?1 AND operation_id = ?2",
+    }
-                params![workspace_id, operation_id],
+
+    fn cancel_current_ticket_coder_assignment(
+        &self,
+        workspace_id: &str,
+        ticket_id: &str,
+        assignment_id: &str,
+        assignment_event_id: &str,
+        state_event_id: &str,
+        operation_id: &str,
+        actor: &str,
+        occurred_at: &str,
+        reason: &str,
+    ) -> Result<bool> {
+        self.with_conn_mut(|conn| {
+            let tx = conn.transaction_with_behavior(TransactionBehavior::Immediate)?;
+            let state: String = tx.query_row(
+                "SELECT workflow_state FROM typed_tickets
+                  WHERE workspace_id = ?1 AND ticket_id = ?2",
+                params![workspace_id, ticket_id],
                 |row| row.get(0),
             )?;
-            if persisted != fingerprint {
+            if !matches!(state.as_str(), "inprogress" | "ready") {
                 return Err(Error::TicketAssignmentConflict(format!(
-                    "operation `{operation_id}` was already used for different Ticket assignment input"
+                    "implementation cancellation requires an inprogress Ticket; current state is `{state}`"
                 )));
             }
-            tx.commit()?;
+            let cleared = clear_current_ticket_role_assignment_in_tx(
-            return Ok(true);
+                &tx,
-        }
-        let deleted = tx.execute(
-            "DELETE FROM ticket_current_worker_assignments
-              WHERE workspace_id = ?1 AND ticket_id = ?2 AND role = ?3 AND assignment_id = ?4",
-            params![workspace_id, ticket_id, role.as_str(), assignment_id],
-        )?;
-        if deleted != 0 {
-            tx.execute(
-                "INSERT INTO ticket_worker_assignment_events (
-                     workspace_id, ticket_id, role, event_id, action, assignment_id,
-                     previous_assignment_id, actor, created_at, operation_id, reason
-                 ) VALUES (?1, ?2, ?3, ?4, 'unassigned', NULL, ?5, ?6, ?7, ?8, ?9)",
-                params![
                 workspace_id,
                 ticket_id,
-                    role.as_str(),
+                TicketAssignmentRole::Coder,
-                    event_id,
                 assignment_id,
+                assignment_event_id,
+                operation_id,
                 actor,
                 occurred_at,
-                    operation_id,
+                Some(reason),
-                    reason,
+                "ticket-role-assignment:cancel-implementation:v1",
-                ],
+            )?;
+            if !cleared {
+                return Ok(false);
+            }
+            if state == "inprogress" {
+                let event_index: i64 = tx.query_row(
+                    "SELECT COALESCE(MAX(event_index), -1) + 1 FROM typed_ticket_events
+                      WHERE workspace_id = ?1 AND ticket_id = ?2",
+                    params![workspace_id, ticket_id],
+                    |row| row.get(0),
+                )?;
+                tx.execute(
+                    "INSERT INTO typed_ticket_events (
+                         workspace_id, ticket_id, event_index, kind, author, at,
+                         from_state, to_state, reason, state_field, heading, body
+                     ) VALUES (?1, ?2, ?3, 'state_changed', ?4, ?5,
+                               'inprogress', 'ready', ?6, 'state',
+                               'Implementation cancelled', '')",
+                    params![workspace_id, ticket_id, event_index, actor, occurred_at, reason],
+                )?;
+                for (key, value) in [
+                    ("event_id", state_event_id),
+                    ("assignment_id", assignment_id),
+                    ("assignment_role", "coder"),
+                    ("operation_id", operation_id),
+                ] {
+                    tx.execute(
+                        "INSERT INTO typed_ticket_event_attributes (
+                             workspace_id, ticket_id, event_index, key, value
+                         ) VALUES (?1, ?2, ?3, ?4, ?5)",
+                        params![workspace_id, ticket_id, event_index, key, value],
                     )?;
                 }
+                let updated = tx.execute(
+                    "UPDATE typed_tickets SET workflow_state = 'ready',
+                             workflow_state_explicit = 1,
+                             queued_by = NULL, queued_at = NULL, updated_at = ?3
+                      WHERE workspace_id = ?1 AND ticket_id = ?2
+                        AND workflow_state = 'inprogress'",
+                    params![workspace_id, ticket_id, occurred_at],
+                )?;
+                if updated != 1 {
+                    return Err(Error::TicketAssignmentConflict(
+                        "Ticket state changed during implementation cancellation".to_string(),
+                    ));
+                }
+            }
             tx.commit()?;
-            Ok(deleted != 0)
+            Ok(true)
         })
     }
 
@@ -5540,6 +5556,117 @@ fn validate_ticket_assignment_role_principal(
     }
 }
 
+#[allow(clippy::too_many_arguments)]
+fn clear_current_ticket_role_assignment_in_tx(
+    tx: &rusqlite::Transaction<'_>,
+    workspace_id: &str,
+    ticket_id: &str,
+    role: TicketAssignmentRole,
+    assignment_id: &str,
+    event_id: &str,
+    operation_id: &str,
+    actor: &str,
+    occurred_at: &str,
+    reason: Option<&str>,
+    fingerprint_domain: &str,
+) -> Result<bool> {
+    let current = read_ticket_role_assignment_by_id(tx, workspace_id, assignment_id)?;
+    let Some(current) = current.filter(|value| value.ticket_id == ticket_id && value.role == role)
+    else {
+        return Ok(false);
+    };
+    let principal_json = serde_json::to_string(&current.principal)
+        .map_err(|error| Error::Store(format!("serialize Ticket assignment principal: {error}")))?;
+    let mut hasher = Sha256::new();
+    for value in [
+        fingerprint_domain,
+        workspace_id,
+        ticket_id,
+        role.as_str(),
+        assignment_id,
+        principal_json.as_str(),
+        actor,
+        reason.unwrap_or(""),
+    ] {
+        hasher.update(value.as_bytes());
+        hasher.update([0]);
+    }
+    let fingerprint = hasher
+        .finalize()
+        .iter()
+        .map(|byte| format!("{byte:02x}"))
+        .collect::<String>();
+    let (principal_id, runtime_id, worker_id) = match &current.principal {
+        TicketAssignmentPrincipal::User { account_id } => (Some(account_id.as_str()), None, None),
+        TicketAssignmentPrincipal::Worker {
+            runtime_id,
+            worker_id,
+        } => (None, Some(runtime_id.as_str()), Some(worker_id.as_str())),
+        TicketAssignmentPrincipal::WorkspaceAgent { agent_key } => {
+            (Some(agent_key.as_str()), None, None)
+        }
+    };
+    let inserted = tx.execute(
+        "INSERT OR IGNORE INTO ticket_assignment_operations (
+             workspace_id, operation_id, action, ticket_id, role, principal_kind,
+             principal_id, runtime_id, worker_id, assignment_id,
+             expected_assignment_id, created_at, request_fingerprint
+         ) VALUES (?1, ?2, 'unassign', ?3, ?4, ?5, ?6, ?7, ?8, ?9, ?9, ?10, ?11)",
+        params![
+            workspace_id,
+            operation_id,
+            ticket_id,
+            role.as_str(),
+            current.principal.kind(),
+            principal_id,
+            runtime_id,
+            worker_id,
+            assignment_id,
+            occurred_at,
+            fingerprint,
+        ],
+    )?;
+    if inserted == 0 {
+        let persisted: String = tx.query_row(
+            "SELECT request_fingerprint FROM ticket_assignment_operations
+              WHERE workspace_id = ?1 AND operation_id = ?2",
+            params![workspace_id, operation_id],
+            |row| row.get(0),
+        )?;
+        if persisted != fingerprint {
+            return Err(Error::TicketAssignmentConflict(format!(
+                "operation `{operation_id}` was already used for different Ticket assignment input"
+            )));
+        }
+        return Ok(true);
+    }
+    let deleted = tx.execute(
+        "DELETE FROM ticket_current_worker_assignments
+          WHERE workspace_id = ?1 AND ticket_id = ?2 AND role = ?3 AND assignment_id = ?4",
+        params![workspace_id, ticket_id, role.as_str(), assignment_id],
+    )?;
+    if deleted != 0 {
+        tx.execute(
+            "INSERT INTO ticket_worker_assignment_events (
+                 workspace_id, ticket_id, role, event_id, action, assignment_id,
+                 previous_assignment_id, actor, created_at, operation_id, reason
+             ) VALUES (?1, ?2, ?3, ?4, 'unassigned', NULL, ?5, ?6, ?7, ?8, ?9)",
+            params![
+                workspace_id,
+                ticket_id,
+                role.as_str(),
+                event_id,
+                assignment_id,
+                actor,
+                occurred_at,
+                operation_id,
+                reason,
+            ],
+        )?;
+    }
+    Ok(deleted != 0)
+}
+
 fn current_ticket_worker_assignment_select_sql() -> String {
     "SELECT a.workspace_id, a.ticket_id, a.assignment_id, a.runtime_id, a.worker_id, \
             a.assigned_by, a.assigned_at \
@@ -11052,18 +11179,58 @@ INSERT INTO worker_registry (
         );
         assert!(
             store
-                .clear_current_ticket_role_assignment(
+                .cancel_current_ticket_coder_assignment(
+                    "workspace-role",
+                    &ticket.meta.id,
+                    "coder-manual-1",
+                    "event-cancel-coder",
+                    "event-cancel-state",
+                    "op-cancel-coder",
+                    "user",
+                    "2026-09-01T00:03:00Z",
+                    "implementation needs to be redone",
+                )
+                .unwrap()
+        );
+        assert!(
+            store
+                .cancel_current_ticket_coder_assignment(
+                    "workspace-role",
+                    &ticket.meta.id,
+                    "coder-manual-1",
+                    "event-cancel-coder-replay",
+                    "event-cancel-state-replay",
+                    "op-cancel-coder",
+                    "user",
+                    "2026-09-01T00:03:30Z",
+                    "implementation needs to be redone",
+                )
+                .unwrap(),
+            "same operation must be idempotent after the assignment is cleared"
+        );
+        let cancelled_ticket =
+            ticket::TicketBackend::show(&backend, ticket.meta.id.clone().into()).unwrap();
+        assert_eq!(
+            cancelled_ticket.meta.workflow_state,
+            ticket::TicketWorkflowState::Ready
+        );
+        assert_eq!(
+            cancelled_ticket
+                .events
+                .last()
+                .and_then(|event| event.attributes.get("assignment_id"))
+                .map(String::as_str),
+            Some("coder-manual-1")
+        );
+        assert!(
+            store
+                .get_current_ticket_role_assignment(
                     "workspace-role",
                     &ticket.meta.id,
                     TicketAssignmentRole::Coder,
-                    "coder-manual-1",
-                    "event-clear-coder",
-                    "op-clear-coder",
-                    "user",
-                    "2026-09-01T00:03:00Z",
-                    Some("test removal guard"),
                 )
                 .unwrap()
+                .is_none()
         );
         assert!(
             store

web/workspace/src/routes/w/[workspaceId]/tickets/[ticketId]/+page.svelte

@@ -55,6 +55,10 @@
   let readyOperationKey = $state<string | null>(null);
   let manualRuntimeId = $state("");
   let manualWorkerId = $state("");
+  let cancellationReason = $state("");
+  const coderAssignment = $derived(
+    ticket.assignments.find((assignment) => assignment.role === "coder") ?? null,
+  );
   const selectedRepository = $derived(
     (loadedRepositories?.items ?? []).find((repository: RepositorySummary) => repository.id === repositoryId) ?? null,
   );
@@ -162,6 +166,18 @@
     });
   }
 
+  async function cancelImplementation(event: SubmitEvent): Promise<void> {
+    event.preventDefault();
+    if (!coderAssignment || !cancellationReason.trim()) return;
+    if (
+      await mutate("cancel-implementation", "/implementation-cancellations", {
+        operation_id: crypto.randomUUID(),
+        assignment_id: coderAssignment.assignment_id,
+        reason: cancellationReason.trim(),
+      })
+    ) cancellationReason = "";
+  }
+
   async function saveEdit(event: SubmitEvent) {
     event.preventDefault();
     if (
@@ -416,6 +432,24 @@
             </button>
           </form>
         {/if}
+        {#if ticket.state === "inprogress" && coderAssignment}
+          <details class="ticket-cancel-implementation">
+            <summary>Cancel implementation</summary>
+            <form class="ticket-control-form" onsubmit={cancelImplementation}>
+              <p class="workspace-empty-copy">
+                Cancel the assigned Coder, remove its assignment, and return this Ticket to ready.
+              </p>
+              <label>Reason<textarea bind:value={cancellationReason} rows="3" required></textarea></label>
+              <button
+                class="workspace-danger-button"
+                type="submit"
+                disabled={busy !== null || !cancellationReason.trim()}
+              >
+                {busy === "cancel-implementation" ? "Cancelling…" : "Cancel and return to ready"}
+              </button>
+            </form>
+          </details>
+        {/if}
         {#if ticket.assignment_diagnostics.length > 0}
           {#each ticket.assignment_diagnostics as diagnostic}
             <p class="workspace-callout">{diagnostic}</p>