fix(effort): per-role floor for --effort resolution + developer→xhigh

resolve_agent_effort returned '' for all agents in prod because empty
ORCH_AGENT_EFFORT_*= env vars clobber pydantic class-defaults, leaving no
non-empty floor to fall back to -> --effort never reached the Claude CLI.

Add a level-4 per-role floor in resolve_agent_effort (src/agents/launcher.py):
_agent_effort_floor reads the declared class-default of agent_effort_<agent>
(model_fields[...].default), which a present-but-empty env cannot override.
Floor applies only when levels 1-3 are empty and BEFORE validation, so a typo
(non-empty) still drops to '' (never-break ORCH-41) and explicit env/override
still wins (priority preserved). config.py: agent_effort_developer high->xhigh
(single source of truth; floor follows automatically).

Refs: ORCH-081

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/config.py

@@ -97,13 +97,15 @@ class Settings(BaseSettings):
     agent_model_deployer: str = ""
 
     # ORCH-41: per-agent effort / reasoning level: low|medium|high|xhigh|max.
-    # Empty -> agent_effort_default. Same resolution order as model. Default split:
-    # thinking agents (analyst/architect/developer/reviewer) -> high; mechanical
-    # agents (tester/deployer) -> medium.
+    # Empty -> agent_effort_default. Same resolution order as model. Default split
+    # (ORCH-081/ORCH-52h): thinking agents (analyst/architect/reviewer) -> high;
+    # developer -> xhigh (coding/agentic role, Opus 4.8 canon); mechanical agents
+    # (tester/deployer) -> medium. These class-defaults are ALSO the per-role floor
+    # used by resolve_agent_effort when the env is empty (single source of truth).
     agent_effort_default: str = "high"
     agent_effort_analyst: str = "high"
     agent_effort_architect: str = "high"
-    agent_effort_developer: str = "high"
+    agent_effort_developer: str = "xhigh"
     agent_effort_reviewer: str = "high"
     agent_effort_tester: str = "medium"
     agent_effort_deployer: str = "medium"