feat(KB-147): add planning and validator model settings

- Extend core Settings types with planningProvider, planningModelId, validatorProvider, validatorModelId fields
- Add model selectors in Settings UI for planning and validator models
- Use planning model for triage task specification generation
- Use validator model for specification review in triage
- Use validator model for code reviews in executor agent
- Update AGENTS.md with model hierarchy documentation

packages/core/src/types.ts

@@ -290,6 +290,22 @@ export interface Settings {
    *  Must be set together with `defaultProvider`. When both are undefined,
    *  the engine uses pi's automatic model resolution. */
   defaultModelId?: string;
+  /** AI model provider for planning/triage (specification) agent.
+   *  Must be set together with `planningModelId`. When both are undefined,
+   *  falls back to `defaultProvider`/`defaultModelId`. */
+  planningProvider?: string;
+  /** AI model ID for planning/triage (specification) agent.
+   *  Must be set together with `planningProvider`. When both are undefined,
+   *  falls back to `defaultProvider`/`defaultModelId`. */
+  planningModelId?: string;
+  /** AI model provider for validator/reviewer agent.
+   *  Must be set together with `validatorModelId`. When both are undefined,
+   *  falls back to `defaultProvider`/`defaultModelId`. */
+  validatorProvider?: string;
+  /** AI model ID for validator/reviewer agent.
+   *  Must be set together with `validatorProvider`. When both are undefined,
+   *  falls back to `defaultProvider`/`defaultModelId`. */
+  validatorModelId?: string;
   /** Default thinking effort level for AI agent sessions.
    *  Controls how much reasoning effort the model uses — higher levels
    *  produce better results but cost more. When undefined, the engine
@@ -342,6 +358,10 @@ export const DEFAULT_SETTINGS: Settings = {
   includeTaskIdInCommit: true,
   defaultProvider: undefined,
   defaultModelId: undefined,
+  planningProvider: undefined,
+  planningModelId: undefined,
+  validatorProvider: undefined,
+  validatorModelId: undefined,
   defaultThinkingLevel: undefined,
   autoResolveConflicts: true,
   smartConflictResolution: true,

packages/dashboard/app/components/SettingsModal.tsx

@@ -269,6 +269,12 @@ export function SettingsModal({
         const selectedValue = form.defaultProvider && form.defaultModelId
           ? `${form.defaultProvider}/${form.defaultModelId}`
           : "";
+        const planningValue = form.planningProvider && form.planningModelId
+          ? `${form.planningProvider}/${form.planningModelId}`
+          : "";
+        const validatorValue = form.validatorProvider && form.validatorModelId
+          ? `${form.validatorProvider}/${form.validatorModelId}`
+          : "";
         return (
           <>
             <h4 className="settings-section-heading">Model</h4>
@@ -279,29 +285,77 @@ export function SettingsModal({
                 No models available. Configure authentication first.
               </div>
             ) : (
-              <div className="form-group">
-                <label htmlFor="defaultModel">Default Model</label>
-                <CustomModelDropdown
-                  id="defaultModel"
-                  label="Default Model"
-                  models={availableModels}
-                  value={selectedValue}
-                  onChange={(val) => {
-                    if (!val) {
-                      setForm((f) => ({ ...f, defaultProvider: undefined, defaultModelId: undefined }));
-                    } else {
-                      const slashIdx = val.indexOf("/");
-                      setForm((f) => ({
-                        ...f,
-                        defaultProvider: val.slice(0, slashIdx),
-                        defaultModelId: val.slice(slashIdx + 1),
-                      }));
-                    }
-                  }}
-                  placeholder="Use default"
-                />
-                <small>Select the AI model used for agent sessions. &quot;Use default&quot; lets the engine choose automatically.</small>
-              </div>
+              <>
+                <div className="form-group">
+                  <label htmlFor="defaultModel">Default Model</label>
+                  <CustomModelDropdown
+                    id="defaultModel"
+                    label="Default Model"
+                    models={availableModels}
+                    value={selectedValue}
+                    onChange={(val) => {
+                      if (!val) {
+                        setForm((f) => ({ ...f, defaultProvider: undefined, defaultModelId: undefined }));
+                      } else {
+                        const slashIdx = val.indexOf("/");
+                        setForm((f) => ({
+                          ...f,
+                          defaultProvider: val.slice(0, slashIdx),
+                          defaultModelId: val.slice(slashIdx + 1),
+                        }));
+                      }
+                    }}
+                    placeholder="Use default"
+                  />
+                  <small>Default AI model used for task execution when no per-task override is set. &quot;Use default&quot; lets the engine choose automatically.</small>
+                </div>
+                <div className="form-group">
+                  <label htmlFor="planningModel">Planning Model</label>
+                  <CustomModelDropdown
+                    id="planningModel"
+                    label="Planning Model"
+                    models={availableModels}
+                    value={planningValue}
+                    onChange={(val) => {
+                      if (!val) {
+                        setForm((f) => ({ ...f, planningProvider: undefined, planningModelId: undefined }));
+                      } else {
+                        const slashIdx = val.indexOf("/");
+                        setForm((f) => ({
+                          ...f,
+                          planningProvider: val.slice(0, slashIdx),
+                          planningModelId: val.slice(slashIdx + 1),
+                        }));
+                      }
+                    }}
+                    placeholder="Use default"
+                  />
+                  <small>AI model used for task planning and specification (triage). Falls back to Default Model when not set.</small>
+                </div>
+                <div className="form-group">
+                  <label htmlFor="validatorModel">Validator Model</label>
+                  <CustomModelDropdown
+                    id="validatorModel"
+                    label="Validator Model"
+                    models={availableModels}
+                    value={validatorValue}
+                    onChange={(val) => {
+                      if (!val) {
+                        setForm((f) => ({ ...f, validatorProvider: undefined, validatorModelId: undefined }));
+                      } else {
+                        const slashIdx = val.indexOf("/");
+                        setForm((f) => ({
+                          ...f,
+                          validatorProvider: val.slice(0, slashIdx),
+                          validatorModelId: val.slice(slashIdx + 1),
+                        }));
+                      }
+                    }}
+                    placeholder="Use default"
+                  />
+                  <small>AI model used for code and specification review. Falls back to Default Model when not set.</small>
+                </div>
+              </>
             )}
             {(() => {
               const selectedModel = availableModels.find(

packages/engine/src/executor.ts

@@ -851,8 +851,9 @@ export class TaskExecutor {
               defaultProvider: settings.defaultProvider,
               defaultModelId: settings.defaultModelId,
               defaultThinkingLevel: settings.defaultThinkingLevel,
-              validatorModelProvider: detail.validatorModelProvider,
-              validatorModelId: detail.validatorModelId,
+              // Per-task validator overrides take precedence over global validator settings
+              validatorModelProvider: detail.validatorModelProvider ?? settings.validatorProvider,
+              validatorModelId: detail.validatorModelId ?? settings.validatorModelId,
               store,
               taskId,
             },

packages/engine/src/triage.ts

@@ -465,8 +465,13 @@ export class TriageProcessor {
           onThinking: agentLogger.onThinking,
           onToolStart: agentLogger.onToolStart,
           onToolEnd: agentLogger.onToolEnd,
-          defaultProvider: settings.defaultProvider,
-          defaultModelId: settings.defaultModelId,
+          // Use planning model settings if both provider and modelId are set, otherwise fall back to defaults
+          defaultProvider: settings.planningProvider && settings.planningModelId
+            ? settings.planningProvider
+            : settings.defaultProvider,
+          defaultModelId: settings.planningProvider && settings.planningModelId
+            ? settings.planningModelId
+            : settings.defaultModelId,
           defaultThinkingLevel: settings.defaultThinkingLevel,
         });
 
@@ -846,6 +851,8 @@ export class TriageProcessor {
       defaultProvider?: string;
       defaultModelId?: string;
       defaultThinkingLevel?: string;
+      validatorProvider?: string;
+      validatorModelId?: string;
     },
   ): ToolDefinition {
     const store = this.store;
@@ -904,6 +911,8 @@ export class TriageProcessor {
               onText: (delta) => options.onAgentText?.(taskId, delta),
               defaultProvider: settings.defaultProvider,
               defaultModelId: settings.defaultModelId,
+              validatorModelProvider: settings.validatorProvider,
+              validatorModelId: settings.validatorModelId,
               defaultThinkingLevel: settings.defaultThinkingLevel,
               store,
               taskId,