content: Phase 5 — rich inline text via structured runs (861/861)

CtText.text may be a list of runs (text marks href); CtHeading/CtQuote rich,
CtCode verbatim. New runs.sx overrides render/markdown/text methods (byte-
identical for plain strings, opt-in). 4 modes: HTML tags / markdown / nested
SX / plain asText (drift-proof). find-replace per-run marks-preserving;
search across run boundaries; CRDT block-granularity LWW; data+wire round-trip.
Runs are a Smalltalk-renderable list (not a dict — substrate can't read dict
fields under nested render dispatch). +36 tests (44 suites). Phase 6 (char-
level inline CRDT) recorded as future.

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

lib/content/find-replace.sx

@@ -10,6 +10,11 @@
 ;; via content/find-replace and a word count over asText stay consistent.
 ;; Immutable; case-sensitive.
 ;;
+;; A text field may be a plain string OR a list of rich-text runs (Phase 5,
+;; run = (text marks href)). fr-rep-text rewrites per run, preserving each run's
+;; marks/href; a match that physically straddles two runs is not joined (the
+;; replacement would have no single mark set) — each run is rewritten in place.
+;;
 ;; Requires (loaded by harness): block.sx, transform.sx (content/map-blocks),
 ;; table.sx (CtTable ivars).
 
@@ -24,6 +29,23 @@
 
 (define fr-rep (fn (s from to) (replace (str s) from to)))
 
+;; rewrite a text-bearing field that is either a plain string or a runs list
+(define
+  fr-rep-text
+  (fn
+    (v from to)
+    (if
+      (list? v)
+      (map
+        (fn
+          (r)
+          (list
+            (fr-rep (nth r 0) from to)
+            (nth r 1)
+            (nth r 2)))
+        v)
+      (fr-rep v from to))))
+
 ;; Blocks whose prose content find/replace rewrites (matches asText's set).
 (define
   fr-has-text?
@@ -66,7 +88,7 @@
                       (if (list? r) (map (fn (c) (fr-rep c from to)) r) r))
                     rs))
                 b1))))
-        (else (blk-set b "text" (fr-rep (blk-get b "text") from to)))))))
+        (else (blk-set b "text" (fr-rep-text (blk-get b "text") from to)))))))
 
 (define
   content/find-replace