Add getLineClass() and getCharHighlights() helpers to bridge alignment
data with inline diff computation for use in the DiffViewer component.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Add --diff-modified-bg and --diff-modified-inline-bg for distinguishing
modified lines from pure additions/deletions in diff view.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Update DiffViewer.svelte to classify lines as removed/added/modified
within changed alignments. Modified lines get a yellow/orange background,
and character-level changes within modified lines are highlighted inline.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

…ffsets

The greedy two-pointer matching in computeLineDiff only advanced the
before pointer on mismatch, causing insertions before a modification to
break pairing. Now peeks at the next after-line when similarity is low;
if it's above threshold, the current after-line is skipped as a pure
insertion and the match proceeds correctly.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Cover computeLineDiff (identical lines, pure additions/removals, modified
line detection, peek-ahead insertion offsets, character highlights, and
complex realistic scenarios), getLineDiffResult caching, getLineClass,
and getCharHighlights helper functions.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

The greedy two-pointer in computeLineDiff only peeked 1 step ahead when
looking for a modified-line match, so re-indented lines preceded by many
insertions (e.g. code wrapped in an if-else block) were misclassified as
removed/added instead of modified. Replace the single peek-ahead with a
forward scan through all remaining unmatched after-lines.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Add a test using exact hunk data from a real diff where code was wrapped
in an if-else block, causing re-indentation. Verifies that context lines
remain unchanged and re-indented lines are classified as modified. Keep
the multi-insertion scan-ahead edge case test separately.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

The line-to-alignment maps stored indices into the changedAlignments
array (filtered subset), but getLineClass/getCharHighlights indexed
into activeAlignments (the full array). This caused lookups to hit the
wrong alignment, so inline diff computation used incorrect line ranges
and failed to detect modifications like re-indentation changes.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

…ified pairs

Character-level LCS inflated similarity scores for unrelated code lines
that shared indentation whitespace (e.g. `r#"<action>"` vs `&branch,`
scored 0.63 due to 8 shared leading spaces). Compare trimmed lines when
computing similarity for line pairing, and raise the threshold from 0.4
to 0.5. This prevents unrelated lines from being classified as
"modified" while preserving detection of re-indentation changes.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

…nent

Limit the greedy matcher's forward scan to 10 unmatched after-lines
(MAX_SCAN_AHEAD) to bound worst-case O(n² × L²) similarity computation.
Replace the module-level cache with a createLineDiffCache() factory so
each DiffViewer component instance owns its cache, preventing stale
entries from previous diffs from occupying slots.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

…d pairs

Lines sharing structural tokens (e.g. JSDoc descriptions with common
words like `segments`, `highlights`) scored 0.515 similarity — just
above the 0.5 threshold — causing unrelated lines to be classified as
"modified" instead of removed/added. Raise threshold from 0.5 to 0.55;
all legitimate modification pairs (re-indentation, single-word edits)
score well above 0.6.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

…tLineDiffResult

The getLineClass/getCharHighlights tests were missing the required
LineDiffCache parameter added in the cache-scoping refactor. Also remove
the deprecated module-level getLineDiffResult singleton — tests now use
createLineDiffCache() directly.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>