fix(fieldtest): probe tier runs on the frontmatter opus model

The owner reviewed the recorded design-review dissent on the probe
tier's sonnet override and agreed with it: field evidence is a
rule-2 judgement role, and the probe cut lacks the deterministic
measurement + verify gate the issue-#30 override rests on. The
probe tier keeps its scope economy (1-2 examples on the single
delta axis, capped report) and drops the model override;
agent-template rule 2 loses the conditioned exception.

refs #35

docs/agent-template.md

@@ -136,16 +136,10 @@ Assignment rule, in priority order:
    gating a cycle (adversarial lenses, plan recon, field/bench
    evidence, the in-loop quality review) — run `opus`. Opus is
    the documented strength for code review, debugging, and deep
-   reasoning. One conditioned exception (issue #35): the
-   per-cycle fieldtest's **probe tier** — the cycle's
-   user-visible delta is a single narrow axis — is dispatched by
-   the `fieldtest` skill with an explicit `model: sonnet`
-   dispatch override; the one-axis scope bounds the judgement
-   surface and the orchestrator triages every finding anyway.
-   The frontmatter keeps the opus default, which the milestone
-   fieldtest always runs. (The direct agent-dispatch surface has
-   no per-dispatch *effort* override, so the frontmatter effort
-   applies unchanged on a probe.)
+   reasoning. This rule covers the fieldtest's probe tier too:
+   a probe narrows *scope*, never the model (a sonnet probe
+   override was ratified and same-day retracted on review
+   grounds — issue #35).
 3. **Mechanical scope** — tightly-scoped execution of a pre-made
    plan, recon, extraction, compliance-diffing run `sonnet`
    (near-opus coding quality at lower latency and cost).

fieldtest/SKILL.md

@@ -86,18 +86,16 @@ probe merely right-sizes the dispatch when the surface delta is
 one axis. A multi-axis cycle takes the full tier — when in
 doubt, full.
 
-**Probe dispatch mechanics.** A probe dispatch passes an
-explicit `model: sonnet` override on the agent dispatch — the
-dispatch-level model override takes precedence over the agent's
-opus frontmatter; the conditioned exception is documented in
-`../docs/agent-template.md` § model, rule 2. (The direct
-agent-dispatch surface has no per-dispatch effort override, so
-the frontmatter effort applies unchanged; the probe's economy
-comes from the model tier and the one-axis scope.) The
-judgement surface a probe covers is one axis, and the
-orchestrator triages every finding anyway. The **milestone
-fieldtest always runs full tier on the frontmatter model** — its
-carrier takes no `tier` field.
+**Both tiers run on the agent's frontmatter model.** A probe
+dispatch changes scope, not model: its economy comes from the
+one-axis cut and the capped report, while finding classification
+stays on the opus judgement tier. (A `model: sonnet` probe
+override was ratified and same-day retracted on review grounds —
+field evidence is a judgement role per
+`../docs/agent-template.md` § model rule 2, and the probe cut
+lacks the deterministic gate the issue-#30 override rests on;
+recorded on issue #35.) The **milestone fieldtest always runs
+full tier** — its carrier takes no `tier` field.
 
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