content: tree-wide content/find + has? (778/778)

Facade read-by-id was top-level only while content/edit's update/delete are
tree-wide — could not read back a nested block content/edit just modified.
Added generic ct-find-id (doc.sx) + doc-find-deep/doc-has-deep?; content/find
+ has? now descend into sections. content/find-top/has-top? keep top-level
lookup. Audit: remaining doc-find/ct-index-of callers are positional
insert/move (top-level by design). +6 api tests.

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

plans/content-on-sx.md

@@ -19,7 +19,7 @@ injected adapter, not core.
 
 ## Status (rolling)
 
-`bash lib/content/conformance.sh` → **772/772** (Phases 1–4 COMPLETE + ~34 extensions, hardened: HTML/SX escaping, Markdown render + import/export incl. tables & frontmatter (full round-trip), CvRDT flat + nested-tree + durable replication, tree-aware validation, snapshot cache, doc metadata, plain-text render, nested block trees + deep editing + flatten + relative reorder, doc stats + summary + multi-doc index, table + callout + media blocks, HTML page wrapper + SEO page, doc composition + id-remap, portable data + wire serialization, block query + transforms + find/replace, TOC + anchored headings + outline, normalization)
+`bash lib/content/conformance.sh` → **778/778** (Phases 1–4 COMPLETE + ~34 extensions, hardened: HTML/SX escaping, Markdown render + import/export incl. tables & frontmatter (full round-trip), CvRDT flat + nested-tree + durable replication, tree-aware validation, snapshot cache, doc metadata, plain-text render, nested block trees + deep editing + flatten + relative reorder, doc stats + summary + multi-doc index, table + callout + media blocks, HTML page wrapper + SEO page, doc composition + id-remap, portable data + wire serialization, block query + transforms + find/replace, TOC + anchored headings + outline, normalization)
 
 ## Ground rules
 
@@ -113,6 +113,19 @@ lib/content/api.sx ── (content/edit) (content/render) (content/history) ─
 
 ## Progress log
 
+- 2026-06-07 — Hardening (tree-wide audit): the public facade `content/find` /
+  `content/has?` were top-level-only (`doc-find`/`doc-has?`), so you could
+  `content/edit` an update/delete to a nested block by id (those ops are
+  tree-wide) but couldn't read that same block back by id through the facade — a
+  concrete read/write asymmetry. Added a generic `ct-find-id` to doc.sx (descends
+  into any `children` list, mirroring ct-replace-id/ct-remove-id, no section.sx
+  dependency) plus `doc-find-deep`/`doc-has-deep?`; `content/find`/`content/has?`
+  now point at them. Kept `content/find-top`/`content/has-top?` for the
+  top-level-only lookup. Audited all `doc-find`/`doc-ids`/`ct-index-of` callers:
+  the remaining ones are insert/move (positional, top-level by design) — no other
+  seams. +6 api tests (nested deep find/has, top variants miss nested,
+  edit-then-find round-trip). 778/778.
+
 - 2026-06-07 — Hardening: `content/diff` (and `content/diff-versions`) are now
   TREE-WIDE. They enumerated ids via `doc-ids`/`doc-find` (top-level only), so a
   diff between two versions of a document containing sections silently missed