feat(agent): add composer final answer

devflow/projects/2026-07-08-executor-composer-final-answer/evidence.md

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+# Evidence
+
+## Relevant History
+
+- `executor-v2-output-contract`: Executor emits structured diagnostic material and no final-expression fields.
+- `executor-gatekeeper-hook`: Gatekeeper validates deterministic evidence failures before Verifier.
+- `executor-verifier-claim-checks`: Verifier emits `claim_checks` and effective verdict guardrails.
+
+## Code Evidence
+
+- `src/main/resources/prompts/chat-composer-prompt.md`: defines Composer as an expression layer with strict JSON output.
+- `src/main/java/com/superbiz/agent/service/ChatService.java`: loads Composer prompt, invokes `chat_composer`, filters Composer input, parses Composer output, falls back safely, and persists Composer audit.
+- `src/test/java/com/superbiz/agent/service/ChatServiceSequentialAgentTest.java`: covers Composer invocation, fallback, REJECT/LOW_CONFID behavior, and no raw JSON leakage.
+
+## Evidence-Driven Conclusions
+
+- Composer must be after Verifier because Verifier `claim_checks` are the authority for allowed final-answer material.
+- Composer must not receive raw tool output or full unscreened Executor output because that would re-open the evidence attribution problem.
+- Verifier malformed/missing output should not invoke Composer because there is no trustworthy decision to filter with.
+- Fixed fallback remains necessary because Composer is an LLM call with a strict JSON contract and can produce malformed output.
+
+## Verification Evidence
+
+Passed:
+
+```powershell
+mvn "-Dtest=ChatServiceSequentialAgentTest" test
+mvn "-Dtest=ExecutorGatekeeperServiceTest,VerifierInputHookTest,ChatServiceSequentialAgentTest" test
+cmd /c openspec validate executor-composer-final-answer
+cmd /c openspec validate --specs
+```
+
+Known existing warnings:
+
+- Maven reports duplicate `spring-boot-starter-test` dependency in `pom.xml`.
+- Existing Lombok `@Builder` default warnings remain.