feat: add max/min count thresholds to sequence rules

[theredspoon]

Closes #1161

Review note: this branch is rebased on #1167 and #1169 (both needed underneath for correctness, see Fix). Only the commit fix(sequence): count-threshold rules dispatch at declared scope, tagging each sentence separately belongs to this PR. Click into it on the Commits tab to see this PR's actual diff. The Files changed tab includes #1167's and #1169's content too, and will shrink once both merge into v3 and this rebases.

Problem

sequence matches tagged patterns but only alerts once per match. It has no count threshold. occurrence has Max/Min but only matches a raw regex, no tag/upos. Root cause: NewSequence unconditionally narrowed every declared scope to sentence-level, so a paragraph with two real matches split across two sentences stayed silent, since each sentence individually had only one match.

tbhb/vale-ai-tells's VerbTricolonDensity.yml needs exactly this. Its occurrence regex can't require the matched words be verbs. A sequence rule can, and now finally gets a count threshold too.

Fix

Run now tags each sentence of a rule's real declared scope separately (reusing internal/nlp/prose.go's existing per-sentence tagging), instead of tagging the whole block once and inferring boundaries afterward. Sentence membership becomes a direct fact, so a match can't span two sentences by construction.

• Threshold rules (Max/Min set) keep their real declared scope instead of being narrowed to sentence-level.
• An undeclared scope on a threshold rule defaults to paragraph plus prose-container scopes, matching plain-rule behavior, via one shared list instead of two hand-copied ones.
• File.Sentences routes through the same local/remote segmentation dispatch the rest of the codebase already uses.

Why the redesign, not a smaller patch (root cause detail)

Sentence boundaries used to be inferred after tagging a whole block once: compare each word's offset against each sentence's own offset. That broke down for a remote endpoint's unpositioned tokens, which carry no offsets to compare. Tagging each sentence separately makes sentence membership a direct fact instead, determined by which loop iteration produced the word.

Performance

Local English tagging: neutral, within noise. Non-English remote endpoint: a plain rule now pays up to 2 round-trips per sentence instead of 1. A separate follow-up, #1170, removes the remaining redundant one for plain rules. Match-walk cost drops from one O(N²) per block to a sum of smaller O(N²/k) terms across k sentences.

Full performance reasoning

For a style's sequence rules as a whole, this is close to neutral for local English tagging. The new per-sentence segmentation pass is cached per file, so only the first rule to touch a sentence pays for it. Every other rule sharing that file's cache gets a hit. One rule against a cold cache measures a few percent slower. Benchmarked with several rules sharing a file's cache, the difference is within noise and can go either way.

sequenceMatches' match-walk is quadratic in the number of words per call. Splitting a block into sentences turns one large quadratic term into a sum of smaller ones, N²/k instead of N² for k sentences. Each sentence also pays a small, fixed per-call cost: tokenization and a fresh lookup map. A block of many very short sentences can let that fixed cost outweigh the quadratic saving. Realistic prose doesn't hit this.

Sentence segmentation is cached: a repeated call against the same text hits a map lookup, measured at roughly 140x faster than a fresh segmentation.

A non-English document behind a remote NLP endpoint pays an extra HTTP round-trip, but not a flat doubling. A plain (sentence-scoped) rule now makes one segmentation call and one tagging call per sentence, two round-trips where there was one before. A max/min rule segments its whole scope in one call, then tags each sentence individually: one extra segmentation round-trip per block rather than per sentence, shrinking as a fraction of the total as a block's sentence count grows. Both calls are cached per file, so a style with many sequence rules pays this once per unique sentence, not once per rule. Local English tagging, the common case, never touches this path at all.

Testing

• cross-sentence aggregation, Max/Min combined
• cross-sentence boundary guard under both local and remote tagging, including a remote tagger normalizing token text
• undeclared-scope threshold rule dispatching into headings and list items
• internal/e2e case (checks/sequence/max) for the density-across-sentences motivating case, end-to-end through a real .vale.ini/style/document

Full repo suite and -race are clean, including internal/e2e. Confirmed no reintroduction of the concurrency risk sequence was historically excluded from concurrent dispatch for.

Alternative considered: extending occurrence.go instead (rejected)

occurrence runs concurrently across rules matching one block. sequence is deliberately excluded from concurrent dispatch because its tagging cache isn't synchronized. Fixable, but it touches shared dispatch infrastructure other check types rely on and gives Occurrence two structurally different matching modes.

Related

min: N per-token repetition (#899) · scope: paragraph fix (#1124/#1126) · remote NLP endpoint panic fixes, split out to #1167 · sentenceScope negated-scope double-report fix, split out to #1169 · redundant round-trip elimination, follow-up in #1170