chore(sep-2640): re-extract against the Final text

src/seps/sep-2640.yaml

@@ -1,5 +1,5 @@
-# spec_source: modelcontextprotocol/modelcontextprotocol@sep/skills-extension seps/2640-skills-extension.md
-# extracted: 2026-08-28
+# spec_source: modelcontextprotocol/modelcontextprotocol@main seps/2640-skills-extension.md
+# extracted: 2026-09-21
 #
 # provenance: re-extracted against the 2026-08-21 revision, which the core
 #   maintainers produced after their second review round and which went back up
@@ -23,15 +23,34 @@
 #   archive rows) and four were reworded. Because the SEP is mid-vote, expect one
 #   more pass at the CM-stamped head.
 #
-# coverage: extracted against branch head a3e147ca2710 (2026-08-25), the commit
-#   the CM vote is running on. A keyword sweep of the source finds 97 sentences
-#   carrying an RFC 2119 term; this file declares 89 checks plus 7 excluded rows.
-#   The residual handful are restatements that fold into a declared row rather
-#   than standing alone. Of the 89 declared checks, 40 are exercised on the wire
-#   by the three server scenarios; the other 49 are host obligations (retrieval
-#   policy, approval binding, cache isolation, context handling) that a
-#   server-side harness cannot observe and that would need a host-side scenario
-#   set to test.
+# final pass: that pass is this one. SEP-2640 was marked Accepted on 2026-09-03
+#   (d6b31a03) and Final on 2026-09-11 (8075db4a), and the source moved from the
+#   sep/skills-extension branch to main. Four commits landed on the text between
+#   a3e147ca and f56f204f, only one of them normative: the Skill Format section
+#   gained a paragraph binding clients to the Agent Skills specification's own
+#   backward-compatibility mechanisms, declared below as two excluded rows.
+#   The Capability Declaration section was reworded to locate the declaration in
+#   the `extensions` field of the server's capabilities rather than loosely in
+#   the `initialize` response, and the `resources`-capability requirement is now
+#   stated there outright instead of being derived from Dependencies; both rows
+#   are restated from the Final text. A copy-editing pass (582d814a) replaced
+#   em-dashes with commas, colons and parentheses throughout, which left twelve
+#   rows quoting text the SEP no longer contains, so those quotes are re-synced.
+#   The design-history links moved with the repository, from
+#   experimental-ext-skills to ext-skills/docs/archive.
+#
+# coverage: extracted against f56f204f6290 on main, the SEP at Final. A keyword
+#   sweep of the source finds 98 sentences carrying an RFC 2119 term; this file
+#   declares 90 checks plus 10 excluded rows. The residual handful are
+#   restatements that fold into a declared row rather than standing alone. Of
+#   the 90 declared checks, 42 are exercised on the wire by the three server
+#   scenarios; the other 48 are host obligations (retrieval policy, approval
+#   binding, cache isolation, context handling) that a server-side harness
+#   cannot observe and that would need a host-side scenario set to test.
+#
+#   The three counts above were 89, 7, 40 and 49 before this pass. Two of those
+#   moved because rows were added; the rest were simply wrong when written, and
+#   nothing recomputes them, so treat them as a claim with a date.
 #
 # deliberately not declared here: `resultType`, which appears in all three
 #   result examples in this SEP, is a base-protocol field on the common `Result`
@@ -78,7 +97,7 @@ requirements:
   # Reverses the retired sep-2640-no-nested-skills row: the June text said a
   # SKILL.md MUST NOT appear in any descendant directory.
   - check: sep-2640-nested-skills-permitted
-    text: 'A `SKILL.md` MAY appear in a descendant directory of a skill — skills can nest.'
+    text: 'A `SKILL.md` MAY appear in a descendant directory of a skill, so skills can nest.'
   - check: sep-2640-nested-skillmd-not-acted-on
     text: "From the enclosing skill's perspective, a nested skill's directory and files are ordinary supporting files, and reading them is ordinary reading. A nested `SKILL.md` read this way is ordinary markdown: hosts MUST NOT act on its frontmatter."
   - check: sep-2640-nested-publication-flat
@@ -100,14 +119,15 @@ requirements:
   # identifiers to per-extension settings objects" and defines no envelope; the
   # SEP-2640 capability block matches it.
   - check: sep-2640-capability-declaration-inline
-    text: 'Per SEP-2133 extension negotiation, servers declare support for this extension in their `initialize` response, mapping the extension identifier directly to its per-extension settings object: `{"capabilities": {"extensions": {"io.modelcontextprotocol/skills": {"directoryRead": true}}}}`.'
+    text: 'Per SEP-2133 extension negotiation, servers declare support for this extension in the `extensions` field of their capabilities, mapping the extension identifier directly to its per-extension settings object: `{"capabilities": {"extensions": {"io.modelcontextprotocol/skills": {"directoryRead": true}}}}`.'
     url: https://modelcontextprotocol.io/seps/2640-skills-extension#capability-declaration
   - check: sep-2640-capability-commits-to-methods
     text: 'Declaring the extension itself commits the server to `skills/list` and `skills/get`.'
   - check: sep-2640-capability-empty-object
     text: 'An empty object indicates support for the extension with no optional features.'
   - check: sep-2640-capability-requires-resources
-    text: "This extension depends only on the base protocol's Resources primitive. Skill files are served through `resources/read`, and the base Resources specification requires any server that supports resources to declare the `resources` capability. A server declaring this extension therefore **MUST** also declare the `resources` capability."
+    text: 'A server declaring this extension MUST also declare the `resources` capability.'
+    url: https://modelcontextprotocol.io/seps/2640-skills-extension#capability-declaration
   - check: sep-2640-capability-directory-read-flag
     text: 'Clients MUST NOT call `resources/directory/read` against a server that has not declared `directoryRead: true`.'
 
@@ -117,15 +137,15 @@ requirements:
   - check: sep-2640-skills-list-pagination
     text: "Pagination mirrors the base protocol's list methods: the request accepts an optional `cursor`, and when the result includes `nextCursor` the client passes it back to retrieve the next page."
   - check: sep-2640-skills-list-entry-atomic
-    text: "An entry is atomic — a skill's `resources` set is never split across pages."
+    text: "An entry is atomic: a skill's `resources` set is never split across pages."
   - check: sep-2640-skills-list-cache-attributes
     text: "In protocol versions 2026-07-28 and later, the result also carries the base protocol's list-caching attributes — `ttlMs` and `cacheScope`, as defined for `tools/list` and `resources/list` (SEP-2549) — with the same semantics: a freshness hint for the listing and a cache-scope marker, not an integrity property."
   - check: sep-2640-skills-list-may-be-partial
     text: 'A server whose skill catalog is large, generated on demand, or otherwise unenumerable MAY return an empty or partial listing.'
   - check: sep-2640-host-no-empty-listing-assumption
     text: 'Hosts MUST NOT treat an empty or partial listing as proof that a server has no skills.'
   - check: sep-2640-enumeration-scheme-uniform
-    text: "The method serves entries for a server's skills whatever URI scheme they use — enumeration is uniform across schemes."
+    text: "The method serves entries for a server's skills whatever URI scheme they use. Enumeration is uniform across schemes."
 
   # === The skill entry (shared by skills/list and skills/get) ===
   - check: sep-2640-entry-uri-required
@@ -141,21 +161,21 @@ requirements:
   - check: sep-2640-names-should-be-unique
     text: "Within a server's listing, names SHOULD be unique, but they are not guaranteed to be."
   - check: sep-2640-host-disambiguate-listing-collision
-    text: 'When two entries in one listing collide on `name`, hosts MUST disambiguate them — for example by their distinguishing path segments — rather than silently discarding or preferring one.'
+    text: 'When two entries in one listing collide on `name`, hosts MUST disambiguate them, for example by their distinguishing path segments, rather than silently discarding or preferring one.'
   - check: sep-2640-names-not-unique
-    text: "A skill's `name` is a label, not an identifier. Within a server's listing, names SHOULD be unique, but they are not guaranteed to be. Hosts MUST NOT assume name uniqueness. When two entries in one listing collide on `name`, hosts MUST disambiguate them — for example by their distinguishing path segments — rather than silently discarding or preferring one."
+    text: "A skill's `name` is a label, not an identifier. Within a server's listing, names SHOULD be unique, but they are not guaranteed to be. Hosts MUST NOT assume name uniqueness. When two entries in one listing collide on `name`, hosts MUST disambiguate them, for example by their distinguishing path segments, rather than silently discarding or preferring one."
 
   # === resources ===
   - check: sep-2640-entry-resources-required
-    text: '`resources` is REQUIRED on every skill entry and takes one of two forms: an array enumerating the skill''s files — `SKILL.md` and every supporting file — as `{uri, digest, size}` triples, or the string `"dynamic"`.'
+    text: '`resources` is REQUIRED on every skill entry and takes one of two forms: an array enumerating the skill''s files (`SKILL.md` and every supporting file) as `{uri, digest, size}` triples, or the string `"dynamic"`.'
   - check: sep-2640-resources-complete
-    text: "When present, `resources` MUST be complete: it lists every file of the skill, each exactly once, including an entry matching the skill's top-level `uri` — that entry carries the digest and size of `SKILL.md` itself."
+    text: "When present, `resources` MUST be complete: it lists every file of the skill, each exactly once, including an entry matching the skill's top-level `uri`. That entry carries the digest and size of `SKILL.md` itself."
   - check: sep-2640-resources-uri-within-skill
     text: "Each `uri` MUST be the skill's `SKILL.md` or a file within the skill's directory."
   - check: sep-2640-resources-digest-format
     text: "Digests are SHA-256 hashes of an artifact's raw bytes, formatted as `sha256:{hex}` where `{hex}` is 64 lowercase hexadecimal characters. Each entry in a skill's `resources` carries the digest of the file at its `uri`."
   - check: sep-2640-resources-size-required
-    text: "Each entry MUST carry `size`: the length in bytes of the file's raw content — the same bytes the `digest` covers."
+    text: "Each entry MUST carry `size`: the length in bytes of the file's raw content (the same bytes the `digest` covers)."
   - check: sep-2640-resources-dynamic-marker
     text: 'When a skill''s content is generated dynamically, such that stable digests cannot be published, the server MUST set `"resources": "dynamic"` instead of an array.'
   - check: sep-2640-resources-invalid-entry
@@ -175,9 +195,9 @@ requirements:
   - check: sep-2640-skills-get-implemented
     text: 'A server declaring the `io.modelcontextprotocol/skills` extension MUST also implement the `skills/get` method, which returns the entry for a single skill named by its URI.'
   - check: sep-2640-skills-get-entry-shape
-    text: 'The `skill` object is a skill entry, identical in shape and meaning to an entry of `skills/list` — the same `uri`, `frontmatter`, and `resources` fields, under the same rules.'
+    text: 'The `skill` object is a skill entry, identical in shape and meaning to an entry of `skills/list`, with the same `uri`, `frontmatter`, and `resources` fields under the same rules.'
   - check: sep-2640-skills-get-unknown-uri-invalid-params
-    text: 'If the URI does not identify a skill the server serves, the server MUST return error `-32602` (Invalid params) — the same code `resources/read` uses for unknown resources.'
+    text: 'If the URI does not identify a skill the server serves, the server MUST return error `-32602` (Invalid params), the same code `resources/read` uses for unknown resources.'
   - check: sep-2640-skills-get-answers-unlisted
     text: 'A server MUST answer for every skill it serves, whether or not that skill appears in its `skills/list` result. A skill absent from a partial listing is still retrievable by URI.'
   - check: sep-2640-skills-get-cache-attributes
@@ -195,7 +215,7 @@ requirements:
   - check: sep-2640-host-size-mismatch-failure
     text: "A read whose byte length differs from the entry's `size` is a verification failure equivalent to a digest mismatch, whether or not the host goes on to compute the digest."
   - check: sep-2640-host-no-prefetch
-    text: "Hosts MUST NOT retrieve a skill's files ahead of need — not on connection, not on listing, and not at approval. A `SKILL.md` is fetched when the skill is loaded, and a supporting file when it is read."
+    text: "Hosts MUST NOT retrieve a skill's files ahead of need, whether on connection, on listing, or at approval. A `SKILL.md` is fetched when the skill is loaded, and a supporting file when it is read."
   - check: sep-2640-host-frontmatter-comparison
     text: "After fetching a `SKILL.md` for which the host holds an entry, hosts MUST parse its YAML frontmatter and compare it field-by-field against the entry's `frontmatter`. Any discrepancy MUST be treated as a verification failure equivalent to a digest mismatch, and the skill MUST NOT be loaded."
   - check: sep-2640-host-digest-not-security-boundary
@@ -280,7 +300,7 @@ requirements:
   - check: sep-2640-directory-read-result-resources-shape
     text: 'The result contains every direct child of the directory: files with their ordinary resource metadata, subdirectories listed as directory resources (`mimeType: "inode/directory"`). The listing is not recursive; clients descend by calling the method again on a child directory.'
   - check: sep-2640-directory-read-invalid-params
-    text: 'The method applies only to directory resources. If the URI does not exist, or exists but is not a directory resource, the server MUST return error `-32602` (Invalid params) — the same code `resources/read` uses for unknown resources.'
+    text: 'The method applies only to directory resources. If the URI does not exist, or exists but is not a directory resource, the server MUST return error `-32602` (Invalid params), the same code `resources/read` uses for unknown resources.'
   - check: sep-2640-directory-read-pagination
     text: 'Pagination mirrors `resources/list`: when the result includes `nextCursor`, the client passes it back as `cursor` to retrieve the next page.'
   - check: sep-2640-directory-read-empty-dir
@@ -289,6 +309,19 @@ requirements:
     text: 'Hosts MUST NOT treat the directory result as extending the manifest. While acting on the skill under the held entry, the host MUST NOT read a newly listed child — an unlisted file is a verification failure, exactly as a digest mismatch is — and MUST NOT surface it to the model as a file of the skill.'
 
   # === Excluded: not observable on the MCP wire ===
+  # Added by the 2026-09-13 Skill Format pass, after this file's first
+  # extraction. Both halves condition on a future incompatible revision of an
+  # external specification, so neither is reachable by a harness today: there is
+  # no such revision to break against, and a client that honors a compatibility
+  # mechanism which has never been exercised is indistinguishable from one that
+  # would ignore it. They are declared so the requirement is tracked rather than
+  # lost, and they become testable the day Agent Skills ships a breaking change.
+  - text: 'In the event that the Agent Skills specification changes in a backwards incompatible way, clients MUST honor any backwards compatibility mechanisms provided by the Agent Skills specification.'
+    excluded: 'Conditioned on a breaking revision of the Agent Skills specification that does not yet exist; there is nothing for a harness to present and nothing for the client to honor.'
+    url: https://modelcontextprotocol.io/seps/2640-skills-extension#skill-format
+  - text: 'Clients SHOULD continue to support the Agent Skills specification as it existed prior to any incompatible change.'
+    excluded: 'Same condition. Supporting a prior revision is observable only against content written to that revision, which requires the incompatible change to have happened first.'
+    url: https://modelcontextprotocol.io/seps/2640-skills-extension#skill-format
   - text: 'Per RFC 3986, the first segment of `<skill-path>` occupies the authority component. This carries no special semantics under this convention and clients MUST NOT attempt DNS or network resolution of it.'
     excluded: 'DNS and network resolution sit below the MCP wire layer; the harness cannot observe whether the client performed name lookups on URI authority components.'
   - text: "Hosts SHOULD indicate which server a skill originates from when presenting it, SHOULD let users inspect a skill's content before it is loaded into model context"
@@ -304,5 +337,5 @@ requirements:
     excluded: 'User-facing messaging; not protocol-observable.'
   - text: 'For a skill whose `resources` is `"dynamic"`, the entry offers nothing to count. A host that chooses to load such a skill applies the total-size limit to what it actually retrieves and MAY stop loading the skill once that limit is reached.'
     excluded: 'A host stopping mid-load is indistinguishable on the wire from a host that needed no further files.'
-  - text: 'Hosts SHOULD expect this sequence and present it as such — a skill that has changed and needs re-approval — rather than as a read error.'
+  - text: 'Hosts SHOULD expect this sequence and present it as a skill that has changed and needs re-approval, rather than as a read error.'
     excluded: 'User-facing presentation of the stale-entry recovery path; not protocol-observable.'