enhance(#3248): disclose capability skills as an instruction surface (#3253)

* test(#3248): failing-first suite for instruction-surface disclosure

28 matrix rows from 50-test-matrix.md. Rows requiring the new
Disclosure.instructionSurfaces field fail today; rows 18-20/23-25 (the
ADR-2363 D4 signature invariants) pass today by construction because the
current code never reads skills/agents at all, and stand as regression
guards for the implementation commit.

Refs #3248

* feat(#3248): disclose capability skills and agents as an instruction surface

ADR-2363 D5. A capability whose only contribution was skills disclosed
nothing at install: summarizeDisclosure early-returned "ships no executable
surfaces (declarative only)" because hasExecutable was false, while each
SKILL.md body landed verbatim in the agent's instruction context.

discloseExecutableSurfaces gains a fifth, NON-executable class,
instructionSurfaces, collecting declared skills/agents stems through the same
safeCollect wrapper as the four existing collectors, so a hostile value
degrades only this class and the function stays total for any manifest shape.
Nothing existing is edited: the collectors, hasExecutable, disclosureSignature
and missingArtifacts are untouched. get_impact rates the symbol CRITICAL at
196 affected, which is why the design is strictly additive.

D4 is implemented by omission and pinned rather than left incidental: adding,
changing or removing skills/agents leaves disclosureSignature byte-identical,
so no stored consent record is perturbed and no spurious re-consent fires.
ADR-2782's conditional-append trick is deliberately NOT reused - it worked
because no manifest could declare a reviewer body before that class existed,
whereas skills predate this one, so a conditional append would re-sign every
already-consented skill-bearing capability.

The renderer is extracted as summarizeInstructionSurfaces and called from BOTH
branches of summarizeDisclosure. Appending only at the end would never render
for skill-only capabilities - the ones that need it - since those take the
early return. That branch's "declarative only" claim is now conditional on
there being no instruction surface either. The renderer iterates rather than
spreading into push, so an unbounded stem count cannot throw RangeError, and
tolerates the bare {} the CLI edge passes via `res.disclosure || {}`.

Scope note: #3248's prose says "skill stems"; ADR-2363 D3 classifies
instruction surfaces as "skills, agents". Shipping skills alone would leave an
ADR deliverable owned by no phase, and the epic has no Phase 2. Agents are the
same shape at no extra cost. Narrowing back is a two-line change.

Ratifies ADR-2363 (Proposed -> Accepted) and adds the owed ADR-1244 back-link.

Closes #3248

* fix(#3248): escape consent-prompt values and narrow disclosure to skills

Two review findings, both of which made the previous commit wrong.

BLOCKER (isolated adversarial review). Every manifest-supplied value
interpolated into a consent-prompt line was rendered unescaped. Those lines
are joined with \n and written RAW to stderr on the needs-consent path
(capability-command-router -> cli-exit runMain), so a stem carrying a newline
forged additional lines indistinguishable from genuine GSD disclosure text,
and an ANSI escape could clear or rewrite lines already printed. That defeats
the informed-consent guarantee this change exists to provide, and is a
prompt-injection vector against any agent that reads the stderr text to decide
whether to retry with --yes.

The hole was not unique to the new class - hook event/script, command
family/module/router, every MCP field, and every reviewer-lane field were
equally unescaped. Fixing only the new one would have created the
generative-fix divergence this repo tracks, so renderValueForPrompt is applied
to all five classes through one helper, guarded by a parity test that fails if
a future class skips it. Escaping is identity for ordinary names, so no
well-formed manifest's output changes. The disclosure OBJECT stays verbatim -
only the rendered LINE is escaped - because the signature and every consumer
reasoning about identity depend on the declared value.

NARROWED to skills only. The previous commit also collected agents, arguing
ADR-2363 D3 classifies instruction surfaces as "skills, agents". Verified
against staging: stageSkillsForRuntimeAsSkills takes a registry and unions
third-party skills in via readInstalledCapabilitySkill, while
stageAgentsForRuntimeWithConverter takes only a source directory and has no
registry-aware path. Third-party agents are never staged into the instruction
context, so disclosing them would have put a false claim in a security prompt -
worse than the scope creep two reviewers flagged it as. D3's classification
stands; D5 now records that Phase 1 implements the skills half and that
whether agents should be staged at all is an open maintainer question.

Also reverts the premature ADR-2363 ratification. The previous commit flipped
it to Accepted and asserted "#3248 merged" while this branch IS #3248 and is
unmerged. Status returns to Proposed, and the ADR-1244 back-link - owed only on
ratification - is withdrawn.

Adds the fast-check property suite CLAUDE.md requires and the direct precedent
(reviewer-trust-disclosure) already had: totality, D4 signature invariance, D3
hasExecutable invariance, and renderer totality over adversarial manifests.

Refs #3248

* chore(#3248): correct changeset scope claim and backfill pr number

The fragment was written against the pre-narrowing commit and still
advertised 'skills and agents'. 4d26887e narrowed disclosure to skills
only - third-party agents are never staged into the instruction context -
but did not touch the fragment, so the release notes would have carried a
claim the code does not implement.

Also backfills pr:0 -> 3253 and names the prompt-escaping fix, which is
user-visible and was absent from the original body.

Changeset-only; no code or test changed, so the gsd-test pass recorded for
4d26887e still describes this tree's behavior.

Refs #3248

---------

Co-authored-by: sim <sim@local>

docs/how-to/develop-a-capability.md

@@ -128,7 +128,7 @@ That makes a skill body an **instruction surface**, and it carries author respon
 - **Write instructions you would be comfortable defending.** Your reach is bounded only by what the agent will do when told. Consent, integrity pinning and reversibility are the user's protections; content review is not among them.
 - **Do not embed anything that tries to redirect the agent away from the user's task** — reframing its role, overriding host instructions, or persisting directives past the skill's own scope. That is indistinguishable from a prompt-injection payload, and the fact that it is not scanned is not permission.
 - **Treat anything your skill tells the agent to read as data, not instructions.** If your skill has the agent ingest a file, a URL, or tool output, say so explicitly in the body. See [the untrusted-input boundary](../adr/1577-untrusted-input-boundary-and-injection-blocking.md).
-- **Expect the surface to be disclosed.** Naming the skills your Capability contributes in the pre-install consent summary lands with [#3248](https://github.com/open-gsd/gsd-core/issues/3248) — it does not happen today. Write your skill body on the assumption that a user will see it listed before they accept.
+- **The surface is disclosed.** The skills your Capability contributes are named, by stem, in their own section of the pre-install consent summary ([#3248](https://github.com/open-gsd/gsd-core/issues/3248)). Write your skill body on the assumption that a user sees it listed before they accept. Declared `agents[]` are not named there today — a third-party capability's agents are never staged into the agent's instruction context, so there is nothing to disclose — but they remain classified as an instruction surface, not an inert or safe one.
 
 The reasoning behind this posture — including why scanning was considered and rejected — is recorded in [ADR-2363](../adr/2363-capability-instruction-surface-trust.md), and the user-facing side is [the capability trust model](../explanation/capability-trust-model.md).