feat(FN-1524): add POST /routines/:id/trigger endpoint

- Add POST /routines/:id/trigger as canonical endpoint for manual routine triggers
- Keep POST /routines/:id/run as backward-compatible alias
- Remove duplicate recordRun calls from routine route handlers (persistence handled by RoutineRunner)
- Update webhook auth to return 401 instead of 403 for signature failures
- Fix TypeScript types for promptOverrides to support null values (delete semantics)
- Fix API endpoint to return empty diff stats when worktree doesn't exist

packages/core/src/prompt-overrides.ts

@@ -457,9 +457,10 @@ export type PromptOverrideEntry = string | undefined;
 
 /**
  * Collection of prompt overrides keyed by PromptKey.
- * Stored in project settings as `promptOverrides: Record<PromptKey, string>`.
+ * Stored in project settings as `promptOverrides: Record<PromptKey, string | null>`.
+ * Null values are interpreted as "delete this override".
  */
-export type PromptOverrideMap = Partial<Record<PromptKey, string>>;
+export type PromptOverrideMap = Partial<Record<PromptKey, string | null>>;
 
 // ---------------------------------------------------------------------------
 // Resolver Functions
@@ -492,8 +493,8 @@ export function resolvePrompt(
   // Check for a valid override
   if (overrides && key in overrides) {
     const override = overrides[key];
-    // Non-empty string is a valid override
-    if (override !== undefined && override !== "") {
+    // Non-empty string is a valid override (null and empty string are treated as "use default")
+    if (override !== undefined && override !== null && override !== "") {
       return override;
     }
   }

packages/core/src/types.ts

@@ -1173,7 +1173,7 @@ export interface ProjectSettings {
    *  Each key maps to a customizable prompt segment (e.g., "executor-welcome",
    *  "triage-context"). When a key is present with a non-empty value, that
    *  override replaces the default prompt segment. Missing or empty values
-   *  fall back to the default prompt content.
+   *  fall back to the default prompt content. Null values delete the key.
    *
    *  This is separate from `agentPrompts` which controls full role templates.
    *  `promptOverrides` allows surgical customization of specific prompt segments
@@ -1182,7 +1182,7 @@ export interface ProjectSettings {
    *  Supported keys: "executor-welcome", "executor-guardrails", "executor-spawning",
    *  "executor-completion", "triage-welcome", "triage-context", "reviewer-verdict",
    *  "merger-conflicts". */
-  promptOverrides?: Record<string, string>;
+  promptOverrides?: Record<string, string | null>;
   /** Enable/disable agent self-reflection workflows. Default: false. */
   reflectionEnabled?: boolean;
   /** How often periodic reflections occur in milliseconds. Default: 3_600_000 (1 hour). */

packages/dashboard/app/components/AgentPromptsManager.tsx

@@ -303,10 +303,9 @@ export function AgentPromptsManager({
   // Handle prompt override change
   const handlePromptOverrideChange = useCallback(
     (key: PromptKey, value: string) => {
-      onPromptOverridesChange({
-        ...promptOverrides,
-        [key]: value || null,
-      });
+      const newOverrides = { ...promptOverrides } as Record<PromptKey, string | null>;
+      newOverrides[key] = value || null;
+      onPromptOverridesChange(newOverrides);
     },
     [promptOverrides, onPromptOverridesChange],
   );
@@ -314,10 +313,9 @@ export function AgentPromptsManager({
   // Handle reset (set to null) for a prompt override
   const handleResetOverride = useCallback(
     (key: PromptKey) => {
-      onPromptOverridesChange({
-        ...promptOverrides,
-        [key]: null,
-      });
+      const newOverrides = { ...promptOverrides } as Record<PromptKey, string | null>;
+      newOverrides[key] = null;
+      onPromptOverridesChange(newOverrides);
     },
     [promptOverrides, onPromptOverridesChange],
   );

packages/dashboard/app/components/SettingsModal.tsx

@@ -2104,10 +2104,10 @@ export function SettingsModal({
                 }));
               }}
               promptOverrides={form.promptOverrides}
-              onPromptOverridesChange={(promptOverrides: Record<PromptKey, string | null> | undefined) => {
+              onPromptOverridesChange={(overrides) => {
                 setForm((f) => ({
                   ...f,
-                  promptOverrides,
+                  promptOverrides: overrides,
                 }));
               }}
             />

packages/dashboard/src/agent-generation.ts

@@ -15,9 +15,9 @@
 import { randomUUID } from "node:crypto";
 
 // Dynamic import for @fusion/core to get prompt override resolution
- 
-type PromptOverrideMap = Record<string, string | undefined>;
- 
+
+type PromptOverrideMap = Record<string, string | null>;
+
 type ResolvePromptFn = (key: string, overrides?: PromptOverrideMap) => string;
 let resolvePrompt: ResolvePromptFn = () => "";
 let promptCatalogReady = false;
@@ -414,7 +414,7 @@ export function parseGenerationResponse(text: string): AgentGenerationSpec {
  *
  * @param ip - Client IP for rate limiting
  * @param roleDescription - The user's description of the desired agent role
- * @returns Session object (without spec — call generateAgentSpec to populate)
+ * @returns Session object (without spec - call generateAgentSpec to populate)
  */
 export async function startAgentGeneration(
   ip: string,

packages/dashboard/src/routes.ts

@@ -116,15 +116,15 @@ export function __setCreateKbAgentForRefine(mock: typeof createKbAgentForRefine)
 }
 
 // Default system prompt for workflow step refinement (fallback when overrides unavailable)
- 
-let resolveWorkflowStepRefinePrompt: (key: string, overrides?: Record<string, string | undefined>) => string = () => DEFAULT_WORKFLOW_STEP_REFINE_PROMPT;
+
+let resolveWorkflowStepRefinePrompt: (key: string, overrides?: Record<string, string | null>) => string = () => DEFAULT_WORKFLOW_STEP_REFINE_PROMPT;
 let promptOverridesReady = false;
 
 async function initPromptOverrides() {
   if (promptOverridesReady) return;
   try {
     const core = await import("@fusion/core");
-    resolveWorkflowStepRefinePrompt = (key: string, overrides?: Record<string, string | undefined>) =>
+    resolveWorkflowStepRefinePrompt = (key: string, overrides?: Record<string, string | null>) =>
       core.resolvePrompt(key as keyof typeof core.PROMPT_KEY_CATALOG, overrides);
     promptOverridesReady = true;
   } catch {