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/reference/capability-manifest.md

@@ -45,6 +45,10 @@ Feature capabilities declare owned artefacts, lifecycle hooks, a federated confi
 | `skills` | string[] | Owned skill stems. Exactly one capability may own each stem across the entire merged registry (first-party ∪ overlay). |
 | `agents` | string[] | Owned agent stems. Same uniqueness constraint as skills. |
 
+The `skills` stems declared here are disclosed by name as **instruction surfaces** in the pre-install consent summary ([ADR-2363](../adr/2363-capability-instruction-surface-trust.md)). Bodies are installed verbatim and are not content-scanned — see [the capability trust model](../explanation/capability-trust-model.md).
+
+`agents` are classified as an instruction surface too (ADR-2363 D3), but the stems declared here are **not** disclosed at the prompt: a third-party capability's `agents[]` are never staged into the agent's instruction context — the staging path that unions third-party skills into a runtime's skills directory has no equivalent for agents — so naming them would claim a surface that does not exist. This does not make agents safe or inert; it means the mechanism does not yet reach them.
+
 ### `hooks`
 
 Non-loop lifecycle hooks.

docs/reference/gsd-capability-command.md

@@ -37,7 +37,7 @@ gsd capability install <spec> [--integrity sha512-<hash>] [--scope global|projec
 
 **Behaviour**
 
-Resolves `<spec>` to a versioned, staged capability bundle. The pipeline is: fetch → verify integrity or SHA pin → check `engines.gsd` against the installed GSD version → disclose executable surfaces (hooks, command modules, MCP servers) → obtain consent (a declarative capability needs none; an executable one requires `--yes`) → validate the incoming manifest against the trust invariants → extract to the scope root → write the ledger entry atomically.
+Resolves `<spec>` to a versioned, staged capability bundle. The pipeline is: fetch → verify integrity or SHA pin → check `engines.gsd` against the installed GSD version → disclose executable surfaces (hooks, command modules, MCP servers) and instruction surfaces (skills) → obtain consent (a declarative capability needs none; an executable one requires `--yes` — disclosed instruction surfaces do not by themselves trigger this requirement) → validate the incoming manifest against the trust invariants → extract to the scope root → write the ledger entry atomically.
 
 An overlay whose `id` uses a reserved first-party prefix (`gsd-`, `gsd-core-`, `anthropic-`) is rejected before extraction. Install never executes capability code; staging is copy-only. A declined install (executable surface, no `--yes`) writes **nothing** — no bundle, no ledger entry, no shared-file edits.
 
@@ -304,6 +304,18 @@ An empty (or missing) ledger reports nothing: `--json` emits `[]`; the table not
 
 ---
 
+### Instruction surfaces (skills)
+
+A capability's declared `skills` stems are **instruction surfaces**: each stem's body — its `SKILL.md` — is copied verbatim into the runtime's instruction context, where it reaches the agent directly. `install` and `update` list every such stem by name in the disclosure printed before the pipeline proceeds, alongside the executable-surface disclosure.
+
+ADR-2363 D3 classifies `agents` as an instruction surface too, but a third-party capability's declared `agents[]` are not disclosed here: they are never staged into the agent's instruction context — the staging path that unions third-party skills into a runtime's skills directory has no equivalent for agents — so naming them would name a surface that does not exist. This is not a claim that agents are safe or inert, only that they are not currently staged for third-party capabilities.
+
+An instruction surface is disclosed but is **not** an executable surface: naming it does not set `hasExecutable` and it does not enter the `disclosureSignature`, so adding, removing, or changing skills between versions does not by itself require `--yes` or force re-consent on `update`. See [ADR-2363](../adr/2363-capability-instruction-surface-trust.md) D3 (the instruction-surface classification) and D4 (why it is excluded from the disclosure signature).
+
+Bodies are not content-scanned, at install, update, or any later point — disclosure names the surface; it never inspects what it contains.
+
+---
+
 ### `trust`
 
 Manage the **user-owned consent store** (#1459) that gates project-scope third-party capability activation. The store lives at `${GSD_HOME||homedir()}/.gsd/consent.json` — **outside any repository** — and records, per `(realpath(projectRoot), capability id)`, the bundle integrity and disclosure signature you consented to **on this machine**. A project-scope overlay is inactive until such a record exists (so a forged or cloned in-repo project ledger activates nothing on its own); installing a project-scope capability through the lifecycle writes the record, and removing it revokes the record.