feat(ui): quieter plan diffs on prose edits (#603)

* feat(ui): atomize balanced emphasis pairs in plan diff

Before word-diffing, replace each balanced `**…**`, `__…__`, `~~…~~`,
`*…*`, `_…_` (and triples `***…***` / `___…___`) with a unique
word-char sentinel — same pattern as the existing code-span / link
atomization passes. Identical phrases pair as unchanged; different
phrases produce a single remove+add.

Fixes the "preliminary analysis" → "final analysis" demo case (⑯),
which previously orphaned the closing `**` into the unchanged tail and
rendered as literal asterisks. Now renders as one clean bold-struck →
bold-green swap.

Pair matching uses CommonMark-ish flanking rules so stray `2**3` or
intraword `my__var` / `snake_case` stay literal. Longest-first ordering
prevents single delimiters from eating the inside of a double-delim pair.

* feat(ui): coalesce adjacent diff sites separated by thin tokens

After `diffWordsWithSpace` and sentinel restoration, merge dirty runs
of ≥2 change sites separated only by thin unchanged tokens (whitespace,
commas, periods, semicolons, colons, dashes, quotes) into a single
phrase-level swap. Parens and brackets are excluded so inline links
and bracketed content stay as hard boundaries.

Turns alternating red/green word-noise (e.g. paragraph reworks with
multiple adjacent word swaps) into a readable before/after. Also
rescues the atomization edge case where wrapping a previously-plain
phrase in emphasis (`foo bar baz` → `foo **bar baz**`) would otherwise
surface as fragmented literal delimiters inside colored tags.

Single-site dirty runs pass through unchanged so isolated word swaps
keep word-level highlighting.

* feat(ui): atomize hyphenated compounds in plan diff

Hyphens between word chars (`ninety-five`, `64-byte`, `state-of-the-art`)
are semantic compound words, not two tokens. `diffWordsWithSpace` splits
on word boundaries, so without this pass `ninety-five` → `ninety-nine`
fragments into an unchanged `ninety-` prefix and a swapped `five`/`nine`
suffix — a visually noisy partial-word diff.

Added a sentinel pass that replaces infix hyphens with a word-char
marker before diffing and restores them afterwards. Runs after the
code/link/emphasis passes so hyphens inside those constructs stay
hidden. Unlike the other sentinels this one uses a fixed marker — all
hyphens restore to the same character, so uniqueness isn't needed.

Leading/trailing dashes and em-dash-like separators (dash with space on
one side) are not substituted; only true compound infixes.

Author: pbowyer

apps/hook/dev-mock-api.ts

@@ -483,9 +483,9 @@ module.exports = { authenticate };
 
 ---
 
-## ⑯ Known Limitation — Word Swap Inside a Multi-Word Bold Phrase
+## ⑯ Fixed — Word Swap Inside a Multi-Word Bold Phrase
 
-> **What to watch for (this is a known glitch):** When a single word inside a multi-word bold phrase changes — like **preliminary analysis** becoming **final analysis** — the engine splits the bold markers across the change boundary. You will likely see raw \`**\` asterisks rendered as literal text and the word "analysis" lose its bold styling. This is a boundary case we haven't fixed yet; it was surfaced by an adversarial audit of the engine.
+> **What to watch for:** When a single word inside a multi-word bold phrase changes — like **preliminary analysis** becoming **final analysis** — the diff engine atomizes the whole balanced \`**…**\` pair so it renders as a clean old-bold-struck + new-bold-green swap. Previously the closing \`**\` orphaned into unchanged-tail text and rendered as a literal asterisk; that limitation is resolved.
 
 Before the leadership steering committee signs off on the external rollout phase, the team must complete a full pass over the **preliminary analysis** of load testing results, confirm that the error budget still permits the planned migration window, and escalate any unresolved dependencies to the program lead. Any open question at this stage must be either resolved or formally deferred to the post-launch review with named owners and dates.
 

packages/editor/demoPlanDiffDemo.ts

@@ -239,9 +239,9 @@ export async function authenticate(request: Request): Promise<AuthContext | null
 
 ---
 
-## ⑯ Known Limitation — Word Swap Inside a Multi-Word Bold Phrase
+## ⑯ Fixed — Word Swap Inside a Multi-Word Bold Phrase
 
-> **What to watch for (this is a known glitch):** When a single word inside a multi-word bold phrase changes — like **preliminary analysis** becoming **final analysis** — the engine splits the bold markers across the change boundary. You will likely see raw \`**\` asterisks rendered as literal text and the word "analysis" lose its bold styling. This is a boundary case we haven't fixed yet; it was surfaced by an adversarial audit of the engine.
+> **What to watch for:** When a single word inside a multi-word bold phrase changes — like **preliminary analysis** becoming **final analysis** — the diff engine atomizes the whole balanced \`**…**\` pair so it renders as a clean old-bold-struck + new-bold-green swap. Previously the closing \`**\` orphaned into unchanged-tail text and rendered as a literal asterisk; that limitation is resolved.
 
 Before the leadership steering committee signs off on the external rollout phase, the team must complete a full pass over the **final analysis** of load testing results, confirm that the error budget still permits the planned migration window, and escalate any unresolved dependencies to the program lead. Any open question at this stage must be either resolved or formally deferred to the post-launch review with named owners and dates.