docs(construct): hard-cap SKILL.md description at 1000 chars in tracked guidance

Promote the description limit from a soft "target <=1000" to a hard 1000-char cap (the loader's absolute limit is 1024; we cap at 1000 for margin) in the two tracked docs: AGENTS.md (the committed digest) and CONTRIBUTING.md (the full workflow). The maintainer-local CLAUDE.md overlay already carries it. Also note in CONTRIBUTING.md that microsoft-rust-guidelines is intentionally user-invocable: false (mandatory auto-load Rust base) so it isn't "fixed" by removing the field.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: UnbreakableMJ

AGENTS.md

@@ -8,12 +8,12 @@ rules that bite. (A maintainer-local `CLAUDE.md` overlay adds host-specific note
 
 ## Hard rules
 
-- **`SKILL.md` frontmatter `description` ≤ 1024 characters.** The loader rejects
-  any skill over the limit (`field 'description' in SKILL.md must be at most
-  1024 characters`). Folded `description: >` blocks render by joining lines with
-  spaces (blank lines → newlines, plus a trailing newline); that *rendered*
-  length is what counts, not the raw line count. Keep a margin — target ≤ 1000.
-  Some descriptions already run close, so re-check after any description edit.
+- **`SKILL.md` frontmatter `description` — hard cap 1000 characters.** The loader's
+  absolute limit is 1024 (`field 'description' in SKILL.md must be at most 1024
+  characters`), but this repo caps the *rendered* description at **1000** — it
+  MUST NOT exceed 1000 chars. Folded `description: >` blocks render by joining
+  lines with spaces (blank lines → newlines, plus a trailing newline); that
+  rendered length is what counts, not the raw line count. Re-check after any edit.
 - **Rebuild BOTH bundles after any skill-dir edit**, in the same commit:
   `<name>.zip` (`zip -qr`, keeps dir entries) and `<name>.skill` (`zip -qrD`,
   drops them). A bundle that lags its `SKILL.md`/`references/` ships broken

CONTRIBUTING.md

@@ -135,11 +135,12 @@ in sync with the subdirectory listing.
 
 ## Editing rules
 
-- **`SKILL.md` frontmatter `description` ≤ 1024 characters (hard limit).** The
-  loader rejects anything longer. YAML folded scalars (`description: >`) join lines
-  with spaces and add a trailing newline, so the **rendered** length is what
-  counts. Keep a margin — **target ≤ 1000** — and re-check after any description
-  edit:
+- **`SKILL.md` frontmatter `description` — hard cap 1000 characters.** The loader's
+  absolute limit is 1024 (it rejects anything longer), but this repo caps the
+  *rendered* description at **1000** — a description MUST NOT exceed 1000 chars.
+  YAML folded scalars (`description: >`) join lines with spaces and add a trailing
+  newline, so the **rendered** length is what counts. Re-check after any
+  description edit:
   ```sh
   python3 - "$skill/SKILL.md" <<'PY'
   import sys
@@ -153,6 +154,11 @@ in sync with the subdirectory listing.
   print(len('\n'.join(out))+1)
   PY
   ```
+- **`microsoft-rust-guidelines` is intentionally `user-invocable: false`.** It is
+  the mandatory auto-load Rust base — `spacecraft-standard` mandates loading it
+  before any Rust and `spacecraft-rust-guidelines` defers to it as "load first," so
+  it fires automatically and is hidden from the `/` menu on purpose. Do **not**
+  remove the field to "fix" a perceived load failure — that is by design.
 - **`README.md` §2 catalogue is load-bearing.** Adding a skill directory means
   adding a matching **alphabetical** row to the table; removing one means deleting
   the row. The README catalogue and the directory list must always agree.