docs(permissions): list the six module pages the landing index omitted (#10339)

`content/docs/permissions/meta.json` ships 21 pages; the "What's in this
module" list in `index.mdx` named 14 of them. The six absent pages —
system-context, delegated-administration, rls, attachments-access,
access-matrix, explain — were routed and in the sidebar, and two were even
described in the overview prose without a link, so nothing was unreachable.
What was wrong is that the one list presenting itself as the module's index
was a partial one with nothing marking it partial.

Each new row is placed at its meta.json position rather than appended: the
existing 14 were already exactly meta.json's order minus the six, so the
order is derived, not invented. Link text is each page's own title (the card
body's "Access Matrix" and "Explain" are slug prettifications; the pages are
titled "Access-Matrix Snapshot Gate" and "Explain Engine"). Three of the six
carry a gloss, matching the existing texture where a gloss is the exception
reserved for a title that under-describes its page.

Answers the card's option (b): the list stays hand-kept, with a comment
naming meta.json as the source of truth and a one-line drift note. meta.json
stores slugs only, so a derived list would have to synthesize link text from
page frontmatter — which measurably regresses at least one existing row, and
loses hand-written glosses that exist in no source file.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DdCnBGcHeufjrq7drTD3wt

Author: claude

content/docs/permissions/index.mdx

@@ -60,18 +60,28 @@ alike — is [Declaring Capabilities](/docs/permissions/capabilities).
 
 ## What's in this module
 
+{/* Source of truth for this module's page set AND its order is meta.json in this directory — routing and the sidebar are built from it, and the list below mirrors it exactly, minus this page. */}
+{/* The list is hand-kept on purpose: meta.json stores slugs only, so the link text and the glosses below exist nowhere else, and a generated list would lose them. */}
+{/* Drift note: nothing checks the two against each other in either direction, so a page added to or removed from meta.json leaves this list silently stale — edit both in the same change. */}
+
 - [Administrator Guide](/docs/permissions/administrator-guide) — the task-first manual for customer system administrators
 - [Authentication](/docs/permissions/authentication)
 - [Social & Enterprise SSO](/docs/permissions/sso)
 - [Authorization Architecture](/docs/permissions/authorization)
+- [System Context (`isSystem`)](/docs/permissions/system-context) — what the platform's one elevation flag short-circuits, and what it deliberately does not
 - [Profiles (removed)](/docs/permissions/profiles)
 - [Permission Sets](/docs/permissions/permission-sets)
 - [Positions](/docs/permissions/positions)
+- [Delegated Administration](/docs/permissions/delegated-administration)
 - [Sharing Rules](/docs/permissions/sharing-rules)
+- [Row-Level Security (RLS)](/docs/permissions/rls)
 - [Field-Level Security](/docs/permissions/field-level-security)
+- [Attachments Access](/docs/permissions/attachments-access)
 - [Permission Metadata](/docs/permissions/permission-metadata)
 - [Declaring Capabilities](/docs/permissions/capabilities) - the package author's half: `defineCapability`, and how `capabilities:` differs from `requires:`
 - [Security Permissions Matrix](/docs/permissions/permissions-matrix)
+- [Access-Matrix Snapshot Gate](/docs/permissions/access-matrix) — the committed (permission set × object) snapshot that makes every grant change a reviewable build event
+- [Explain Engine](/docs/permissions/explain) — ask the runtime why one decision came out the way it did, layer by layer
 - [Record-View Auditing](/docs/permissions/record-view-auditing) - who opened which record, and when
 - [Access Recipes](/docs/permissions/access-recipes)