fix(heartbeat): align response tool prompts (#76458)

* fix(heartbeat): align response tool prompts

* docs(changelog): credit heartbeat prompt fix

qa/scenarios/models/codex-harness-no-meta-leak.md

@@ -11,7 +11,7 @@ coverage:
     - runtime.no-meta-leak
 objective: Verify the Codex app-server harness keeps coordination/meta chatter out of the visible reply.
 successCriteria:
-  - The scenario forces the Codex embedded harness and disables PI fallback.
+  - The scenario forces the Codex embedded harness.
   - The final visible reply includes the requested confirmation token.
   - The visible reply does not include internal coordination or progress chatter.
 docsRefs:
@@ -29,7 +29,6 @@ execution:
     requiredProvider: codex
     requiredModel: gpt-5.5
     harnessRuntime: codex
-    harnessFallback: none
     expectedReply: QA_LEAK_OK
     prompt: |-
       Think through your answer privately, but do not expose any internal planning, thread-context checks, or progress narration.
@@ -76,8 +75,6 @@ steps:
                         agentRuntime:
                           id:
                             expr: config.harnessRuntime
-                          fallback:
-                            expr: config.harnessFallback
             - call: waitForGatewayHealthy
               args:
                 - ref: env
@@ -94,11 +91,7 @@ steps:
                 expr: "snapshot.config.agents?.defaults?.agentRuntime?.id === config.harnessRuntime"
                 message:
                   expr: "`expected agentRuntime.id=${config.harnessRuntime}, got ${JSON.stringify(snapshot.config.agents?.defaults?.agentRuntime)}`"
-            - assert:
-                expr: "snapshot.config.agents?.defaults?.agentRuntime?.fallback === config.harnessFallback"
-                message:
-                  expr: "`expected agentRuntime.fallback=${config.harnessFallback}, got ${JSON.stringify(snapshot.config.agents?.defaults?.agentRuntime)}`"
-    detailsExpr: "env.providerMode === 'live-frontier' ? `provider=${selected?.provider} model=${selected?.model} runtime=${snapshot.config.agents?.defaults?.agentRuntime?.id} fallback=${snapshot.config.agents?.defaults?.agentRuntime?.fallback}` : `mock mode: parsed ${scenario.id}`"
+    detailsExpr: "env.providerMode === 'live-frontier' ? `provider=${selected?.provider} model=${selected?.model} runtime=${snapshot.config.agents?.defaults?.agentRuntime?.id}` : `mock mode: parsed ${scenario.id}`"
   - name: keeps codex coordination chatter out of the visible reply
     actions:
       - if:

qa/scenarios/workspace/medium-game-plan-codex-harness.md

@@ -12,7 +12,7 @@ coverage:
 objective: Verify the Codex app-server harness can plan and build a medium-complex self-contained browser game.
 successCriteria:
   - A live-frontier run fails fast unless the selected primary model is openai/gpt-5.5 with the Codex harness forced.
-  - The scenario forces the Codex embedded harness and disables PI fallback.
+  - The scenario forces the Codex embedded harness.
   - The prompt explicitly asks the agent to enter plan mode before editing.
   - The agent writes a self-contained HTML game with a canvas loop, controls, scoring, waves, pause, and restart.
 docsRefs:
@@ -30,7 +30,6 @@ execution:
     requiredProvider: codex
     requiredModel: gpt-5.5
     harnessRuntime: codex
-    harnessFallback: none
     artifactFile: star-garden-defenders-codex.html
     gameTitle: Star Garden Defenders
     minBytes: 5000
@@ -81,8 +80,6 @@ steps:
                         agentRuntime:
                           id:
                             expr: config.harnessRuntime
-                          fallback:
-                            expr: config.harnessFallback
             - call: waitForGatewayHealthy
               args:
                 - ref: env
@@ -99,11 +96,7 @@ steps:
                 expr: "snapshot.config.agents?.defaults?.agentRuntime?.id === config.harnessRuntime"
                 message:
                   expr: "`expected agentRuntime.id=${config.harnessRuntime}, got ${JSON.stringify(snapshot.config.agents?.defaults?.agentRuntime)}`"
-            - assert:
-                expr: "snapshot.config.agents?.defaults?.agentRuntime?.fallback === config.harnessFallback"
-                message:
-                  expr: "`expected agentRuntime.fallback=${config.harnessFallback}, got ${JSON.stringify(snapshot.config.agents?.defaults?.agentRuntime)}`"
-    detailsExpr: "env.providerMode === 'live-frontier' ? `provider=${selected?.provider} model=${selected?.model} runtime=${snapshot.config.agents?.defaults?.agentRuntime?.id} fallback=${snapshot.config.agents?.defaults?.agentRuntime?.fallback}` : `mock mode: parsed ${scenario.id}`"
+    detailsExpr: "env.providerMode === 'live-frontier' ? `provider=${selected?.provider} model=${selected?.model} runtime=${snapshot.config.agents?.defaults?.agentRuntime?.id}` : `mock mode: parsed ${scenario.id}`"
   - name: builds the medium game artifact
     actions:
       - if:

qa/scenarios/workspace/medium-game-plan-pi-harness.md

@@ -30,7 +30,6 @@ execution:
     requiredProvider: openai
     requiredModel: gpt-5.5
     harnessRuntime: pi
-    harnessFallback: pi
     artifactFile: star-garden-defenders-pi.html
     gameTitle: Star Garden Defenders
     minBytes: 5000
@@ -81,8 +80,6 @@ steps:
                         agentRuntime:
                           id:
                             expr: config.harnessRuntime
-                          fallback:
-                            expr: config.harnessFallback
             - call: waitForGatewayHealthy
               args:
                 - ref: env