* docs(#3247): record the capability instruction-surface trust model
ADR-2363 records the trust posture for third-party capability SKILL.md
bodies, which #2322/#2340 made agent-invocable without any content-level
control. The path-level protections that fix shipped are all present; no
content scanner exists, and external-descriptor-trust.cts never had one.
Nothing was bypassed - the control did not exist and the boundary was
never written down.
D1 records the posture: skill bodies are trusted, unscanned agent
instructions. D2 rejects content scanning on Kerckhoffs (a shipped rule
set is readable by the adversary who installs it), on threat-model
non-transfer from ADR-1577 (there, instructions are anomalous inside
data; here they are the payload's legitimate form), and on Goodhart (a
scanned-OK line displaces the judgment the consent prompt exists to
provoke). D3 replaces the executable/non-executable binary with three
classes, adding instruction surface.
D4 keeps instruction surfaces out of the v1 disclosureSignature. The
signature is NOT the activation binding - hasProjectConsent compares
contentHash only, and a global install carries no consent record at all.
What re-encoding would do is perturb the signature of every skill-bearing
capability and fire a spurious re-consent prompt on its next upgrade,
which is what ADR-2782 D4 rule 5 already forbids. If instruction surfaces
ever need to be signature-bound, that lands as a versioned v2 signature
with a migration, never an in-place re-encoding.
Corrects capability-trust-model.md, which claimed skills get lighter
consent because they do not execute code - true, and not the relevant
property, since the agent is the interpreter. Adds the author-side
boundary to develop-a-capability.md and links it from
publish-a-capability.md. Both state that per-skill disclosure at the
consent prompt lands with #3248 and does not happen today.
Docs-only. No behavior change; no consent record perturbed. D5's
mechanism is Phase 1 (#3248), which is why the ADR is Proposed.
Refs #2363
* chore(#3247): backfill changeset pr number to 3249
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Co-authored-by: sim <sim@local>
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