feat(agents): pin explicit reasoning effort on every agent and workflow call

Effort joins model as a mandatory pin: an omitted field inherits the
session effort, coupling every dispatch's thinking budget to whatever
the user happens to be chatting at (often xhigh) — the same
session-state coupling the model pin removes. The assignment follows
the model split:

- xhigh on every opus agent (judgement roles are the pipeline's
  quality floor and must not degrade with the session);
- high on every sonnet agent (tightly-scoped plan execution gains
  little from xhigh but pays its latency per dispatch, and these are
  the per-task in-loop roles — wall-clock is the efficiency metric;
  not lower than high, since re-loops cost more than saved thinking);
- medium inline in the workflow scripts for schema-bound
  extraction/verification stages that author no code (preflight,
  plan-extract, mini-verify, tree-check, finalize, build/suite
  verify).

Workflow agent() calls pass effort explicitly on every call — whether
frontmatter effort propagates through an agentType dispatch is
undocumented, so the scripts do not rely on it. Policy documented in
docs/agent-template.md § effort, mirroring § model.

docs/agent-template.md

@@ -13,6 +13,7 @@ name: <agent-slug>
 description: <third-person, "Use when…" or role description>
 tools: <comma-separated tool list>
 model: <opus | sonnet>
+effort: <xhigh | high>
 ---
 
 > Violating the letter of these rules is violating the spirit.
@@ -137,6 +138,34 @@ The same rule binds Workflow scripts: every `agent()` call passes an
 explicit `model:` option (see the model-policy header comments in
 `implement/workflows/*.js`).
 
+### `effort`
+
+Mandatory. Every agent pins an explicit reasoning effort — one of the
+harness levels `low | medium | high | xhigh | max`, of which the plugin
+uses two. An omitted field means the agent inherits the *session*
+effort, coupling every dispatch's thinking budget to whatever the user
+happens to be chatting at — the same session-state coupling the `model`
+pin exists to remove. Effort follows the model split:
+
+- **`xhigh` on every `opus` agent.** The judgement roles are the
+  pipeline's quality floor; their thinking budget must not silently
+  degrade because the session runs lower.
+- **`high` on every `sonnet` agent.** Tightly-scoped execution of a
+  pre-made plan gains little from `xhigh` but pays its latency on
+  every dispatch — and these are exactly the roles dispatched
+  per-task inside loops (wall-clock is the pipeline's efficiency
+  metric). Not lower than `high`: a sloppy in-loop step triggers
+  re-loops that cost more wall-clock than the saved thinking.
+
+Workflow scripts pin a third tier inline: schema-bound
+extraction/verification stages that author no code (preflight,
+plan-extract, mini-verify, tree-check, finalize, build/suite verify)
+run `medium` via the `agent()` call's `effort:` option. As with
+`model:`, every `agent()` call passes `effort:` explicitly — whether
+frontmatter effort propagates through an `agentType` dispatch is
+undocumented, so the scripts do not rely on it (see the policy header
+comments in `implement/workflows/*.js`).
+
 ## Sections in detail
 
 ### Spirit-letter lead-in