fix(gateguard): make the external-contract question opt-in

- questionIdsFor and condensedHintFor take an optional
  { externalContract: true }; without it a code change that handles data
  asks data-schema only, and an unknown profile gets the original four
  questions and condensed hint.
- The hook reads GATEGUARD_EXTERNAL_CONTRACT_QUESTION with the same
  spellings as GATEGUARD_METRICS and passes it to the full denial, the
  condensed denial and the metrics record, so all three agree.
- The effectiveness harness's arm patch forwards the option, so an arm
  never drops it silently.

Docs: change-profile.md gains an External-contract question section and
qualifies "byte-identical to the fixed four questions"; design-notes.md,
SKILL.md (switch table, data rule, word-for-word set) and CHANGELOG say
the fifth question is opt-in; question-effectiveness.md and the harness
README note that the runner clears GATEGUARD_* variables, so a gate arm
from a current tree measures the gate without the question.
skill-triggers@1.json: registryDigest refreshed for the SKILL.md body
change; the description and triggers are unchanged.

docs/gateguard/change-profile.md

@@ -116,6 +116,21 @@ or a PowerShell file or web cmdlet (`Out-File`, `Get-Content`,
 `*-Clixml`; `Import-Csv` matches `csv`). Redirection is found without
 reading quotes, so a `>` inside a string also counts.
 
+## External-contract question
+
+`GATEGUARD_EXTERNAL_CONTRACT_QUESTION` (`1`, `true`, `on`, `enabled`,
+`enable` or `yes`) adds `external-contract` right after every `data-schema`
+in the table above: "Name what outside this repository decides the format,
+units, timezone or protocol semantics here (the consumer, the producer, or a
+stated convention), or state that the choice is unconstrained". The condensed
+hint and the decision metrics name it too. It is off by default because it
+has no evidence behind it: it was designed after inspecting the
+hidden-intent corpus, and in the rerun that added it the gated arm did not
+improve (see
+[question-effectiveness.md](question-effectiveness.md#adding-an-external-contract-question-did-not-help)).
+`questionIdsFor(class, isWrite, profile, { externalContract: true })` returns
+the ids with it.
+
 ## Trivial edits
 
 An Edit is trivial when, for every entry, old and new have the same code once
@@ -293,7 +308,8 @@ questions were asked without storing text.
 | config | any | `config-reader`, `config-effect`, `no-plaintext-secrets`, `quote-instruction` |
 
 `[data-schema]` is asked only when `touchesData`. With an unknown profile the
-code text is byte-identical to the fixed four questions. Sensitive and
+code text is byte-identical to the fixed four questions, unless the opt-in
+[external-contract question](#external-contract-question) is on. Sensitive and
 hard-linked targets and NotebookEdit calls are never profiled, so they always
 get the full code questions. Instruction and
 config questions carry no change-dependent item, and the test and prose items

docs/gateguard/design-notes.md

@@ -207,7 +207,9 @@ their absolute path. A Windows-style path has no real location on a POSIX host
 The first matching class wins: instruction, test, prose, config, code (the
 fallback). Cursor `.mdc` rule files are instructions wherever they live. A
 basename starting with `.env` is config unless it has a code extension
-(`.env.example.ts` is source). Code targets ask the original four questions,
+(`.env.example.ts` is source). Code targets ask the original four questions
+(five with the opt-in
+[external-contract question](change-profile.md#external-contract-question)),
 narrowed by the change profile (see
 [Questions from the change profile](change-profile.md#questions-from-the-change-profile)); other
 classes get class-specific questions and a class-specific condensed hint.

docs/gateguard/question-effectiveness.md

@@ -529,6 +529,14 @@ and the corpus suggests that kind of answer matters. What is not claimed is
 that adding it improved anything measurable here. A fair test needs scenarios
 written by independent authors who have not seen that question or these results.
 
+Because nothing here shows it helps, the question is now opt-in: it is asked
+only with `GATEGUARD_EXTERNAL_CONTRACT_QUESTION` on (see
+[change-profile.md](change-profile.md#external-contract-question)). The
+harness clears every `GATEGUARD_*` variable from the agent's environment, so a
+`gate` arm built from a candidate tree that includes this change measures the
+gate without it, the "before the question" condition above. The runs reported
+here used candidate trees from before the change, where it was always asked.
+
 **Standing conclusion.** Across 336 billed trials the gate's benefit is not
 established, its direction has been positive in the unflagged runs, and its cost
 is a consistent 35 to 45% in turns and spend. "Not confirmed" is not "no