feat(fase3): make the maker-checker checker actually gate the reasoning

Closes gap #3 (maalbilde §5): the GroupChat checker critiqued into the void —
output_from=[proposer] surfaced only the proposer, so an explicit checker
rejection was ignored and the deterministic validator was the sole gate. Two
falsifiers now act on the same candidate: the validator gates the NUMBERS
(blocking, unchanged), the checker gates the REASONING (maalbilde §2/§6).

- workflow.py: output_from=agents surfaces both participants; the checker
  instruction ends with a VERDICT: APPROVE / VERDICT: REJECT - <reason> line.
- run.py: _authored_texts() reads author_name through out.messages (MAF 1.9.0
  puts it there, not on the AgentResponse); _debate_text() now selects the
  PROPOSER-authored output (fixes a latent texts[-1] regression that would feed
  the checker's verdict to generation at even round counts); _checker_verdict()
  parses the gate decision. An explicit REJECT overrides an otherwise-validated
  outcome to a checker-sourced Rejection. Opt-in-reject (fail-open on a missing
  marker). RunResult gains checker_verdict; provenance.validator_decision is
  stamped from the validator outcome BEFORE the override, so it never conflates
  the two falsifiers (provenance honesty).

Load-bearing (maalbilde §7): tests/test_checker_gate_loadbearing.py is a PAIR —
an explicit checker REJECT on a VALIDATOR-VALID proposal yields a Rejection whose
reason carries the checker's reason while validator_decision stays "validated";
the causality control (checker APPROVE, same proposer) validates normally. Proven
RED on BOTH detach points (revert output_from, or drop the override).

Suite 134->136 passed, 4 skipped; mypy + ruff check clean. Pre-existing
ruff-format drift (backends/budget/verdicts/test_contracts) left untouched for a
surgical diff.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MHR8iKxJRxDiDfNw8HZmWE

src/portfolio_optimiser/workflow.py

@@ -26,7 +26,12 @@ from agent_framework.orchestrations import GroupChatBuilder
 _MAKER_CHECKER_ROLES = ("proposer", "checker")
 _INSTRUCTIONS = {
     "proposer": "You propose one concrete cost-saving measure for the project.",
-    "checker": "You critique the proposal and flag any constraint violation.",
+    "checker": (
+        "You critique the proposal's reasoning and flag any constraint violation. "
+        "End your reply with exactly one verdict line: 'VERDICT: APPROVE' if the reasoning "
+        "holds, or 'VERDICT: REJECT - <short reason>' if it does not. The validator gates the "
+        "numbers; your verdict gates the reasoning (Step 3/4 — målbilde §2)."
+    ),
 }
 
 
@@ -79,10 +84,11 @@ def fresh_workflow(
     is called once per role, so each run owns its own clients — no state survives between runs.
 
     ``tools`` + ``middleware`` are attached to each agent (F2/F7; constructed by the
-    orchestrator). ``output_from=[proposer]`` makes ``WorkflowRunResult.get_outputs()`` surface
-    the proposer's converged output — without it, ``get_outputs()`` yields only the
-    orchestrator's "reached max rounds" notice, so the F1 debate->generation dataflow could not
-    read the debate result (verified against installed 1.9.0).
+    orchestrator). ``output_from=agents`` makes ``WorkflowRunResult.get_outputs()`` surface BOTH
+    participants' converged outputs — the proposer's (fed to generation, F1) AND the checker's
+    gate verdict (Step 3/4); ``run.py`` separates them by per-message ``author_name``. Without it,
+    ``get_outputs()`` yields only the orchestrator's "reached max rounds" notice (verified against
+    installed 1.9.0).
     """
     agents = maker_checker_agents(client_factory, tools=tools, middleware=middleware)
     # Agents are built from _MAKER_CHECKER_ROLES in order with name=role, so the role tuple
@@ -100,9 +106,10 @@ def fresh_workflow(
         selection_func=select,
         # Safety net well above the hard cap; with_max_rounds is the binding bound (B4).
         termination_condition=make_termination(max_rounds * len(names) + 1),
-        # Surface the PROPOSER's converged output so get_outputs() carries the debate
-        # result (F1); the default surfaces only the orchestrator's termination notice.
-        output_from=[agents[0]],
+        # Surface BOTH participants so get_outputs() carries the proposer's converged output
+        # (fed to generation, F1) AND the checker's gate verdict (Step 3/4); run.py separates
+        # them by author_name. The default surfaces only the orchestrator's termination notice.
+        output_from=agents,
     ).with_max_rounds(max_rounds)
     if enable_layer1_hitl:
         # Layer-1: in-run synchronous review on the checker (no checkpoint — research 01).