fix: wire generated_by_model into observation write path

The generated_by_model column was added to the observations table in the
Phase 0 governance schema migration but never wired into the INSERT
statements. All 3,878+ observations in production have this field NULL.

This fix threads the model ID from each agent (SDKAgent, GeminiAgent,
OpenRouterAgent) through processAgentResponse() into storeObservation(),
storeObservations(), and storeObservationsAndMarkComplete().

Unblocks Thompson Sampling RFC (#1571) which needs {obs_type}:{model}
as the bandit arm key.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/services/worker/GeminiAgent.ts

@@ -175,7 +175,9 @@ export class GeminiAgent {
           worker,
           tokensUsed,
           null,
-          'Gemini'
+          'Gemini',
+          undefined,
+          model
         );
       } else {
         logger.error('SDK', 'Empty Gemini init response - session may lack context', {
@@ -248,7 +250,8 @@ export class GeminiAgent {
               tokensUsed,
               originalTimestamp,
               'Gemini',
-              lastCwd
+              lastCwd,
+              model
             );
           } else {
             logger.warn('SDK', 'Empty Gemini observation response, skipping processing to preserve message', {
@@ -298,7 +301,8 @@ export class GeminiAgent {
               tokensUsed,
               originalTimestamp,
               'Gemini',
-              lastCwd
+              lastCwd,
+              model
             );
           } else {
             logger.warn('SDK', 'Empty Gemini summary response, skipping processing to preserve message', {

src/services/worker/OpenRouterAgent.ts

@@ -131,7 +131,8 @@ export class OpenRouterAgent {
           tokensUsed,
           null,
           'OpenRouter',
-          undefined  // No lastCwd yet - before message processing
+          undefined,  // No lastCwd yet - before message processing
+          model
         );
       } else {
         logger.error('SDK', 'Empty OpenRouter init response - session may lack context', {
@@ -202,7 +203,8 @@ export class OpenRouterAgent {
             tokensUsed,
             originalTimestamp,
             'OpenRouter',
-            lastCwd
+            lastCwd,
+            model
           );
 
         } else if (message.type === 'summarize') {
@@ -244,7 +246,8 @@ export class OpenRouterAgent {
             tokensUsed,
             originalTimestamp,
             'OpenRouter',
-            lastCwd
+            lastCwd,
+            model
           );
         }
       }

src/services/worker/SDKAgent.ts

@@ -270,7 +270,8 @@ export class SDKAgent {
             discoveryTokens,
             originalTimestamp,
             'SDK',
-            cwdTracker.lastCwd
+            cwdTracker.lastCwd,
+            modelId
           );
         }
 

src/services/worker/agents/ResponseProcessor.ts

@@ -54,7 +54,8 @@ export async function processAgentResponse(
   discoveryTokens: number,
   originalTimestamp: number | null,
   agentName: string,
-  projectRoot?: string
+  projectRoot?: string,
+  modelId?: string
 ): Promise<void> {
   // Track generator activity for stale detection (Issue #1099)
   session.lastGeneratorActivity = Date.now();
@@ -102,7 +103,8 @@ export async function processAgentResponse(
     summaryForStore,
     session.lastPromptNumber,
     discoveryTokens,
-    originalTimestamp ?? undefined
+    originalTimestamp ?? undefined,
+    modelId
   );
 
   // Log storage result with IDs for end-to-end traceability