fix(parameterization): word-boundary check prevents over-eager value match

ParameterizationPreview.tokenize() matched highlight values via raw
seg.text.startsWith(value, cursor) with no word-boundary check and no
minimum length. A param value like "D" (e.g. a drive letter) lit up every
capital D in the script body — Get-ADUser, Add-Type, Disable- all rendered
as proposed-parameter pills.

Add a word-boundary guard: a candidate match is only accepted if either
side of the match either falls at start/end of the segment, OR the
adjacent character is non-alphanumeric. The guard is conditional on
whether the value itself starts/ends with a word char, so values that
begin or end in punctuation (e.g. "D:\\Folder") still match cleanly when
they sit next to whitespace or punctuation.

Surfaced 2026-05-01 while testing the suggested-fix flow with a real
PowerShell script.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/components/pilot/script/ParameterizationPreview.tsx

@@ -80,10 +80,27 @@ function tokenize(body: string, highlightValues: Record<string, string> | undefi
     while (cursor < seg.text.length) {
       let matched: { key: string; value: string } | null = null
       for (const [key, value] of valueEntries) {
-        if (seg.text.startsWith(value, cursor)) {
-          matched = { key, value }
-          break
-        }
+        if (!seg.text.startsWith(value, cursor)) continue
+        // Word-boundary guard: a single-char value like "D" (drive letter)
+        // would otherwise light up every capital D in identifiers like
+        // `Get-ADUser`. We only require a boundary on a side of the value
+        // that itself starts/ends with a word char, so values that begin or
+        // end in punctuation (e.g. "D:\\Folder") still match cleanly.
+        const valueStartsWithWordChar = /^\w/.test(value)
+        const valueEndsWithWordChar = /\w$/.test(value)
+        const before = cursor > 0 ? seg.text[cursor - 1] : undefined
+        const after = cursor + value.length < seg.text.length
+          ? seg.text[cursor + value.length]
+          : undefined
+        const startBounded = !valueStartsWithWordChar
+          || before === undefined
+          || !/\w/.test(before)
+        const endBounded = !valueEndsWithWordChar
+          || after === undefined
+          || !/\w/.test(after)
+        if (!startBounded || !endBounded) continue
+        matched = { key, value }
+        break
       }
       if (matched) {
         flushPending()