[boyan01]

Summary

Small fixes found while reviewing mixin_markdown_widget. No architecture change. This is the base of a stack; the selection refactor builds on top.

 appendChunk(chunk)
   reparse tail block
-    id = kind-count-hash(content)        # new id every chunk → remount, caches dropped
+    id = previous tail id (same kind-count, nested too, images excluded)

 MarkdownCodeHighlightCache.resolve(streamed code)
-  placeholder = plain text               # flashes plain each chunk
-  compute() per chunk
+  placeholder = last highlight + plain suffix
+  one highlight in flight per block, then run the latest source

 MarkdownDocumentView.build
-  dispose all link recognizers           # cached list/quote rows keep disposed ones
+  one recognizer per LinkInline, disposed when the link leaves the document
-  onTapLink identity change → clear row cache
+  rows call a stable forwarder; cache cleared only when links turn on/off

 double click
-  ASCII separator set                    # Chinese text selects a whole run
+  + CJK punctuation; non-ASCII runs narrow to ICU word boundaries

Also:

• currentState as dynamic in the document view → internal MarkdownSelectableBlockHandle interface.
• New MarkdownController.updateData(data, {streaming}): appends when data extends the current data, else full parse; commits unless streaming.
• @Deprecated: MarkownWidget alias, MarkdownDocumentParser.parseAppending (ignores previousDocument).

Evidence

• Before: streaming ids churned on every chunk:

  "Hello"     → paragraph-2-1968976203
  " world"    → paragraph-2-1498229191
  " again\n"  → paragraph-2-114815919
  

  markdown_link_recognizer_test.dart fails against the old lib/: the cached - [link](url) row holds a recognizer that was already disposed.
  After: ids stay the same across appends (paragraph, fenced code, list and its item children); the recognizer test passes.
• flutter analyze: no issues. flutter test: 214 passed (192 existing, unchanged expectations + 22 new in markdown_controller_streaming_test, markdown_code_highlight_cache_test, markdown_link_recognizer_test, markdown_word_selection_test).
• benchmark/incremental_append_benchmark.dart: baseline 112 ms → 107 ms, large-prefix 60 ms → 63 ms (noise).
• Not covered by automation: visual highlight flicker and real-device CJK word segmentation (flutter_tester ICU has no CJK dictionary, so tests assert dictionary-independent properties).

Merge Danger

Door: two-way

Internal changes plus one additive API and two deprecations; reverting is a plain revert.

Blast Radius: streaming

Apps that stream markdown see the tail block keep its state instead of remounting. Highlight placeholders may briefly show a stale last token (e.g. an unclosed string) until the real highlight lands. codeBlockBuilder / bulletBuilder changes still do not invalidate cached rows (pre-existing).