ocr_stabilizer 0.9.0

Real-time OCR overlay stabilization engine — drift correction, spatial indexing, block tracking. Pure Dart; Flutter-ready.

0.9.0 - 2026-07-23

Validation release for the opt-in agreementWeighted model (#58 data arc): production-capture replay across three stream regimes (stable / reflow / heavy OCR jitter), two numerics fixes, and the replay tooling that produced the evidence. Default behavior is unchanged — legacy consumers can upgrade without review.

Changed (opt-in agreementWeighted numerics only)

• The agreement scale is now a jitter allowance: 3× the regional median block height (#70, #73). The 0.7.0 drift-margin-derived scale was removed: median-of-drift is a systematic-offset measure — ~0 under symmetric jitter and pure numeric residue on stable streams — so it collapsed position confidence on unmoving blocks (1.0 → 0.34, fixed by the #70 floor) and was unreachable everywhere else. Separately, the sweep showed the un-tuned 1× fallback scale let the confidence-anchored merge weight chase deep-chain jitter at 15.8 px/merge (worse than legacy). Post-change: deep-chain jitter damps to 3.8 px/merge (legacy: 11.8) while confidence stays regime-discriminating (~1.0 stable / 0.85 reflow / 0.35 heavy jitter). Sweep evidence: doc/replay/validation/2026-07-scale-sweep/. Slated to become the 1.0 default (#74).

Added

• Replay rig for consumer-captured observation streams (#68): dart tool/replay/replay.dart <freeze-report|ab-report|live-report> <capture.jsonl> grades captured streams against the engine — freeze semantics (#57), position-model A/B (#58), and consumer-side lifecycle views. JSONL schema contract: doc/replay/capture_schema.md.

Decided

• Provisional-freeze semantics stay evidence-free (#57, #69, #76): frozen captures accrue no observation count, text votes, or position. Decision + re-armed re-open triggers are codified at the freeze path; the one nonzero-traffic counterfactual observed (noisy-OCR dwell, admit-mode replay) was tail magnitude — 1 chain, 3 freezes, 2 discarded high-confidence votes per ~5-minute session.

0.8.0 - 2026-07-22

The package is now pure Dart (#59): no Flutter SDK dependency, usable in server-side Dart (PDF and camera OCR pipelines) and CLI tools as well as Flutter apps. Same behavior, new geometry types — read the migration notes below.

Breaking

• Geometry types moved off dart:ui. Rect, Offset, and Size are now package-owned value types exported from the barrel (lib/src/types/geometry.dart), member-compatible with their dart:ui counterparts and matching their semantics exactly (strict overlaps on edge-touching rects, negative-size intersect for disjoint rects, Rect.lerp incl. null-scaling branches). Migration:
  • Code constructing package inputs: change the import — call sites are unchanged.
  • Flutter render boundary: convert with ui.Rect.fromLTRB(r.left, r.top, r.right, r.bottom) and the reverse (copy-paste extensions in the README's Platform Support section).
• Debug logging is opt-in. BlockClassifierService and DriftTracker take a debugLogger: void Function(String)? constructor parameter (default null = silent) instead of calling Flutter's debugPrint. Pass debugLogger: print to restore the previous output.
• pubspec surface: the flutter SDK dependency and flutter: '>=3.19.0' environment constraint are gone; dev-deps are test + lints (replacing flutter_test + flutter_lints — the effective lint rule set is unchanged, flutter_lints layered Flutter-widget rules this package never triggered).

Internal

• CI runs on dart natively: latest stable plus a Dart 3.3 floor leg (replacing the Flutter 3.19 floor leg — same floor, expressed in the SDK that now matters). Coverage artifact retained.
• All 520 tests pass under plain dart test on both legs; zero Flutter packages in dependency resolution.

0.7.0 - 2026-07-22

Additive release: the opt-in agreementWeighted position-merge prototype (#58). Default behavior is unchanged — ^0.6.0 consumers can upgrade without review.

Added

• PositionMergeModel enum and StabilizationEngine(positionMergeModel: ...) (#58). The default legacy preserves 0.x numerics exactly. The opt-in agreementWeighted prototype addresses the audit §1.7 findings:
  • Merge weight decays with observation count (fresh / (existing·n + fresh)): long-observed blocks become positionally sticky — a 6-times-confirmed block barely moves for a single 12px outlier — while young blocks still adapt quickly.
  • Merged confidence is a running mean of positional agreement (residual vs the region's drift margin, median-block-height scaled when no margin exists) instead of the saturating sum: disagreeing observations now reduce confidence, making qualityScore's position term informative again for well-observed blocks. Rollout mirrors the band-fallback pattern: ship on legacy, A/B agreementWeighted against your captures, adopt when the numbers hold. Slated to become the 1.0 default pending that validation.

0.6.1 - 2026-07-21

Performance release finishing the remaining #55 items. No API changes.

Performance

• Intra-batch NMS now resolves overlaps against a per-batch spatial grid instead of linearly scanning the whole output per fresh block — ~O(n²)·(drift-margin per pair) becomes O(cells) (#55). Behavioral nuance: the grid applies the same 3×3-neighborhood locality contract the inter-capture matching path already uses, so two blocks whose centers sit more than one bucket apart are no longer compared — only observable for blocks wider than ~2 buckets, which the spatial index documented as out-of-contract in 0.5.1.
• stabilize() reuses that batch grid for grouping-contradiction detection instead of building a second throwaway index every capture (#55). The public detectGroupingContradictions now sizes its temporary index's buckets from the engine's spatial index rather than defaults.
• DriftTracker.medianDriftForKey / medianBlockHeightForKey / driftMarginForKey cache per-key results, invalidated on addObservation and every clearing path — previously each call copied and sorted up to 20 samples, several times per block per capture (#55).

Internal

• CI uploads the lcov coverage report as a build artifact from the latest-stable leg (#60; badge/coverage-service wiring still open there — needs a repo token).
• flutter_lints constraint comment updated for the Dependabot-widened >=4.0.0 <7.0.0 range (#63): 4.x resolves on the Dart 3.3 floor, newer lines elsewhere.
• Test count: 513.

0.6.0 - 2026-07-20

Audit-driven feature-and-fix release implementing the 0.6.0 roadmap (#46–#56). Pre-1.0, behavioral changes take a minor bump: review the Breaking section before upgrading from 0.5.x.

Breaking

• CssSubmapMembership.spaceKeyFor maps viewport-relative (weight 40) and nested IC+carousel (weight 30) blocks to SpaceKey.unknown() instead of SpaceKey.normal(...) (#48). Drift observation and correction are now symmetric: a position:fixed header no longer receives the page-scroll submap's median correction it never contributed to. Consumers relying on VR blocks being drift-corrected (unlikely — the correction was categorically wrong) must supply a custom SubmapMembership.
• ContradictionEvent's constructor is no longer const and throws ArgumentError when evidence has fewer than 2 entries (#51) — the storage-invariant policy (throw, not assert) now applies here too. Migration: drop const from any ContradictionEvent constructions (engine-produced events are unaffected).
• Contradiction detectors skip the viewport-relative boundary (#49): detectGroupingContradictions ignores VR cached blocks and detectSplittingContradictions ignores VR fresh blocks. Near scroll offset 0, healthy sticky headers were reported as "subdivided" by unrelated normal blocks and evicted by consumers.
• Batch-NMS key lifecycle (#50): dedup keys register only for blocks that survive intra-batch NMS, and an evicted block's key retires with it. Dropped blocks no longer fuzzy-suppress later same-neighborhood blocks. Eviction lookup is identity-based — Equatable-style consumer blocks can no longer cause the wrong value-equal element to be replaced.
• New direct dependency meta: ^1.11.0; dev-dependency flutter_lints moved ^5.0.0 → ^4.0.0 because 5.x requires Dart 3.5 and never actually resolved on this package's declared ^3.3.0 floor — caught by the new CI floor leg (#56).

Added

• StabilizationEngine.missedFrameRetention (#46): opt-in retention window keeping unmatched cached blocks matchable for N further stabilize() calls, so a single OCR miss (glare, occlusion) no longer resets a block's accumulated identity. Default 0 preserves 0.5.x behavior exactly; retained blocks are never part of stableBlocks. The stabilize() index-ownership docs now tell one consistent story.
• StabilizationEngine.updateViewport(...) (#52): single validated entry point that recomputes the spatial index's adaptive buckets and adopts the same dimensions for dedup keys. The bucketWidth / bucketHeight / scale setters now throw ArgumentError on non-finite or non-positive values.
• DriftTracker.propagationCountFor(spaceKey) — public reader for the counts written via recordPropagation (#53).
• TextVote implements == / hashCode / toString, matching the package's other value types (#53).
• BandFallbackStatsInternal is annotated @internal — the analyzer now flags downcast-mutation from outside the package (#53).

Deprecated

• DriftTracker.spaceKeys — use the identical observedKeys; removal planned for 1.0 (#53).

Fixed

• DriftTracker.clearKey / clearSpatialRegion now also clear the matching propagation counts, which previously leaked for the rest of the session (#55).

Performance

• Text-similarity calls (isTextSimilar, isTextSimilarWithScores, computeTextSimilarity) extract each string's significant-char list once and feed both metric cores — previously up to 6 extractions per comparison (#55).

Internal

• CI matrix now tests the declared minimum floor (Flutter 3.19.6) alongside latest stable (#56); Dependabot covers GitHub Actions and pub (#60).
• Band admission ordering caveat and String.hashCode key-stability caveat documented (#53).
• Test backfill (#54): first dedicated suites for RobustStats, IqrOutlier, OverlapResolver, BlockKeyGenerator, AbsoluteRect, hierarchy/scroll value types, CssSubmapMembership, and TextVote; real mixed-confidence coverage for computeTextConfidence; regression tests for every fix above. Test count: 504 (was 297), verified on both stable and Flutter 3.19.6.

0.5.1 - 2026-07-20

Bug-fix release driven by the v0.5.0 package audit (doc/audit/2026-07-20-package-audit.md in the repository). No API changes — ^0.5.0 consumers resolve 0.5.1 automatically.

Fixed

• SpatialBlockIndex.candidates() now deduplicates yielded blocks by object identity, matching allBlocks / blocksInRegion. Previously a dual-indexed IC block reachable from both its page-absolute cell and its ic: cell was yielded twice to an IC query — running the full Levenshtein comparison twice per duplicate and double-ticking the BandFallbackStats funnel counters (candidatesConsidered, rejectedSpatial, rejectedTextBand, and in observeOnly bandMatchesIdentified) that consumers are told to read before flipping to admit.
• StabilizationEngine primary matching no longer drops a candidate admitted purely through the Jaccard arm with a Levenshtein score of 0.0 (full character reordering, e.g. a two-character OCR segment swap like 北京 → 京北). The best-candidate scan seeded its comparison at 0.0 with a strict >, so such a match never registered and the observation spawned a duplicate block instead of merging.
• OcrBlock now stores a NaN confidence as null (unavailable). The documented clamp could not contain NaN — in IEEE-754, nan.clamp(0.0, 1.0) returns NaN — so NaN leaked to any consumer reading confidence directly. Infinite values still clamp to the range bounds.
• Unified the package's two divergent CJK-ideograph definitions into one shared predicate (lib/src/internal/cjk_ideographs.dart). The dedup utilities (cjkOnly, cjkFraction, significant-char extraction) omitted CJK Extension B (U+20000–U+2A6DF) while the confidence heuristic included it, so text consisting only of Extension-B ideographs produced an empty significant-char list and could never text-dedup. TextDedupUtils and isCjkIdeograph now agree.

Documentation

• StabilizationEngine.stabilize documents the index-rebuild limitation: blocks not re-observed in a capture leave the spatial index and re-enter as new; app-inserted blocks are dropped at the next call. The cache-merge redesign is tracked for 0.6.0.
• classifyGroups documents its silent fallbacks (degenerate imageToLayoutScale → identity CSS-per-px; near-singular container transform → untransformed rect) and the actual positionLookup throw contract (caught, neutral stability — previously documented as "must not throw").
• SpatialBlockIndex.blocksInRegion documents the center-cell + 1-cell-margin lookup limit for oversized blocks; remove() documents that cell keys are recomputed from the current rect, so removal after mutation silently no-ops.
• TextDedupUtils.containmentRatio documents the 5,000-rune LCS truncation on the public API (was only on the private helper) and drops a stale internal-caller claim.
• RobustStats.madOrFallback scopes its "never zero or negative" guarantee to positive minSpread.
• MergeResult.observationCount documents the provisional-freeze exception (count passes through unchanged while frozen).

Internal

• .pubignore added: internal process docs (doc/superpowers/, doc/audit/) no longer ship in the published package archive.
• Full package audit report at doc/audit/2026-07-20-package-audit.md (repository only).
• First dedicated test file for TextDedupUtils (test/text_dedup_utils_test.dart). Test count: 297 (was 277).

0.5.0 - 2026-05-24

Quality-polish release. Additive public-API additions plus a latent engine bug fix in the band-fallback counter accounting. No breaking changes from 0.4.x — ^0.5.0 is a safe upgrade.

Added

• BandPredicateException — typed wrapper class for throws raised by a consumer-supplied BandSpatialPredicate. The engine catches the predicate's error inside _findMatch and rewraps it as BandPredicateException(cause, predicateStackTrace). Predicate failures now surface with a typed shape; no silent swallow. Exposes cause, predicateStackTrace, message, and an asserting ctor that rejects double-wrapping (#35).
• BandFallbackStats.rejectedTextBand counter ticks at the text-band-miss site inside _findMatch. Makes the band funnel decomposable: rejectedCandidateFloor + rejectedSpatial + rejectedTextBand + bandMatchesIdentified == candidatesConsidered, invariant to admit-mode early-exit (#34).
• Library-level dartdoc in lib/ocr_stabilizer.dart now enumerates the headline types (StabilizationEngine, BandFallbackConfig, BandFallbackStats, BandPredicateException, block hierarchy, confidence types) plus the recommended adoption flow (off → observeOnly → admit) (#35).
• Internal assertConfidenceRange(field, raw, {prefix}) utility at lib/src/internal/confidence_validation.dart centralises the [0.0, 1.0] finite-double predicate. Adopted at five sites: DefaultTrackedBlock ctor, MergeResult ctor, StabilizationEngine._assertValidConfidence (called by stabilize and merge), PositionConfidence.from, TextConfidence.from. Future tightening happens in one place (#31).

Changed

• BandFallbackStats.matchesAdmitted is now incremented at the resolution-time site (where _findMatch actually returns a band match), not at scan-time. Before this release, the counter ticked as soon as a candidate was locked as bandAdmitted — so when a later primary candidate in the same scan superseded it, the counter overcounted and disagreed with the function's return value. New semantics: matchesAdmitted is exactly "band matches returned by _findMatch", and the documented invariant matchesAdmitted <= bandMatchesIdentified is strengthened by the precedence rule "primary always wins, even if a band candidate was locked first" (#34).
• MergeResult ctor's confidence-range error message wording upgraded from 'must be in [0.0, 1.0]' to 'must be a finite double in [0.0, 1.0]' to match the message at the engine entry guard and DefaultTrackedBlock ctor — a consumer catching ArgumentError no longer sees two slightly different stories about the same invariant (#31).

Fixed

• Library dartdoc no longer references a non-existent stabilize(fresh, captureRect) signature — the actual signature is stabilize(List<T> freshBlocks). Caught by the comment-analyzer pass on PR #42 (#35).
• Privacy scrub: removed 17 references to the downstream consumer's internal project name / file:line paths from spec/plan docs and one source comment (#33).

Internal

• New CI job: pana scoring on ubuntu-latest with --exit-code-threshold 0 pinned to pana 0.23.12. Authoritative pre-publish score check — Windows local pana hits 150/160 due to upstream dart-lang/dartdoc issue #4180 (CRLF offsets in Flutter SDK @docImport files), but Linux scoring is 160/160 (#36).
• Renamed docs/ → doc/ for the Pub layout-convention hint (#37).
• Test count: 277 (was 270 in v0.4.0).

0.4.0 - 2026-05-23

Added

• BandFallbackMode enum (off | observeOnly | admit) configures the band-relaxed fallback path inside StabilizationEngine._findMatch. Default is off; switch to observeOnly to read BandFallbackStats before committing to admit. See doc/superpowers/specs/ for the full design and default provenance (#20).
• BandFallbackConfig value type wraps the band thresholds, candidate observation floor, provisional-capture grant, and spatial confirmation predicate. Constructor asserts on out-of-range values (preserves const-constructibility); engine constructor throws ArgumentError for release-build safety. Primary-path floors (Lev 0.70 / Jaccard 0.80) are engine-owned, not configurable through this type (#20).
• BandFallbackStats exposes per-capture counters: primaryMatchesAdmitted, primaryMatchesRejected, candidatesConsidered, rejectedCandidateFloor, rejectedSpatial, bandMatchesIdentified, matchesAdmitted. Read-only public surface; engine mutates via a same-library Internal subclass. Reset via reset(); the engine never resets it automatically (#20).
• BandSpatialPredicate typedef mirrors ContextualInvalidationCheck — bool Function(TrackedBlock fresh, TrackedBlock candidate). When BandFallbackConfig.spatialConfirm is null, the engine substitutes a drift-aware overlapRatio >= 0.80 closure (#20).
• StabilizationEngine constructor gains a bandFallback: BandFallbackConfig parameter (defaults to mode: off — backward compatible) and a bandStats getter returning the read-only stats view (#20).

Changed

• Breaking: StabilizationEngine.stabilize() and StabilizationEngine.merge() now throw ArgumentError if any observation's positionConfidence.raw or textConfidence.raw is NaN or outside [0.0, 1.0]. Catches any TrackedBlock implementor at the engine entry, closing the documented unchecked-const-Confidence gap (#27).
• Breaking: DefaultTrackedBlock constructor throws ArgumentError when positionConfidence.raw or textConfidence.raw is NaN or outside [0.0, 1.0]. Early-fail at construction with a cleaner stack trace than the engine-entry guard would produce. Consumers going through PositionConfidence.from() / TextConfidence.from() (validated since #19) are unaffected (#27).
• StabilizationEngine._findMatch primary path now uses TextDedupUtils.isTextSimilarWithScores (Lev OR Jaccard) instead of normalizedLevenshtein alone. Floors are unchanged (Lev 0.70 / Jaccard 0.80); the metric set widens — character-reordered text with the same significant-character set now matches on the primary path where it previously fell through (#20).

Fixed

• OverlapResolver.qualityScore no longer silently propagates NaN into the NMS comparison. NaN reaching qualityScore is now a debug-time AssertionError; release builds skip the check (defended by engine entry validation, above) (#27).
• StabilizationEngine constructor now rejects NaN and ±Infinity for BandFallbackConfig.bandLevenshteinFloor and bandJaccardFloor in release builds. The bare range check (value < 0 || value >= floor) evaluated false for NaN under IEEE 754 and let it bypass the defense; the assert in the const ctor catches it in debug only. Now short-circuits on !isFinite before the range check (#20).

0.3.0

A breaking release bundling four API changes. Pre-1.0, breaking changes take a minor version bump.

Breaking

• ObservableBlock no longer declares exclusionHitCount, and DefaultTrackedBlock no longer carries it. The field was inert engine-side — never read or written by merge, dedup, drift correction, or the spatial index. It is consumer-managed state and does not belong on the package's block contract. Migration: a consumer with @override int get exclusionHitCount; on its own block class removes the @override annotation — the field stays, it is just no longer an interface member. Consumers that do not need the field drop it entirely. (#23)
• PositionConfidence.from / TextConfidence.from now throw ArgumentError on out-of-range or NaN input. Previously they validated with assert only, which is stripped in release builds — an invalid confidence passed silently in production. Migration: catch ArgumentError instead of AssertionError; any code that relied on release-mode silent acceptance of an out-of-range value now gets a thrown exception. The primary const PositionConfidence(double) / const TextConfidence(double) constructor stays public and unchecked — it is the only const-capable path, kept for const literal sentinels. (#26)

Changed

• StabilizationEngine.stabilize() now rebuilds spatialIndex internally from its returned stableBlocks before returning. The old caller contract (call spatialIndex.rebuild(result.stableBlocks) after every stabilize()) is retired, along with the debug-mode staleness guard. Callers can drop the post-stabilize() rebuild call — a redundant rebuild is harmless, so this is non-breaking. (#24)
• MergeResult's confidence boundary checks now also reject NaN (NaN fails both < 0 and > 1.0, so it previously slipped through). (#26)

Added

• StabilizationEngine.resetDriftPropagation() — clears the engine's regional-drift baseline so a consumer can reset propagation state on a session boundary (page navigation, context reset) without a stale baseline triggering a spurious correction. (#25)

0.2.2

Added

• CI: GitHub Actions workflow running flutter analyze + flutter test on push and PR (#15).
• CONTRIBUTING.md documenting dev setup, conventions, and release flow (#16).

0.2.1

Docs + metadata polish. No API change. First pub.dev-shipped release of the v0.2.x line.

Documentation

• README: install snippet updated to ^0.2.1 with a breaking-change pointer back to the 0.2.0 typed-confidence migration. (#14)
• README: TrackedBlock<T> example now lists all 14 getters (was missing innerScrollerTop, sourceQuality) with a follow-up note pointing integrators at DefaultTrackedBlock<T> or ObservableBlock<T> as appropriate. (#14)
• README: API Reference tables refreshed for v0.2.x — corrected getter count, generic on ObservableBlock<T>, documented DefaultTrackedBlock<T>, PositionConfidence, TextConfidence, plus the previously-undocumented exports (StabilizationEngine, BlockClassifierService, OverlapResolver, BlockKeyGenerator, MergeResult, StabilizationResult, ClassificationResult, TextVote, IqrOutlier, TextDedupUtils). (#14)

Metadata

• pubspec.yaml gains homepage: and pub.dev topics: (ocr, overlay, tracking, slam, flutter). (#14)
• .gitignore excludes local agentic-scaffolding directory (.ultra/). (#14)

0.2.0

Breaking

• TrackedBlock.positionConfidence and textConfidence now return typed PositionConfidence / TextConfidence extension types (over double) instead of raw double. Consumers implementing TrackedBlock must update the getter signatures. The migration path:

  - final double positionConfidence;
  - final double textConfidence;
  + final PositionConfidence positionConfidence;
  + final TextConfidence textConfidence;
  

  Producer sites wrap raw doubles via .from(value) (range-asserted), or use the .groundTruth sentinel (= 1.0) for deterministic origins. Extension types are zero-cost at runtime.

Added

• PositionConfidence / TextConfidence extension types in lib/src/types/confidence_types.dart. Range [0.0, 1.0] enforced via .from() factory; .groundTruth static const sentinel for DOM/deterministic origins. (#10)
• DefaultTrackedBlock<T> — concrete reference implementation of ObservableBlock<T> with documented defaults for every required field (notably carouselIdVotes: {-1: 1} — the engine's phantom-vote sentinel). Includes copyWith and applyMerge(MergeResult) convenience. (#5)
• SpatialBlockIndex.isEmpty — O(1) accessor (was: allBlocks.isEmpty allocated a Set.identity() per call). (#2)
• StabilizationEngine.stabilize() debug-mode staleness warning when the spatial index appears empty after a non-empty previous call, plus prominent "Caller contract" docstring documenting the consumer's rebuild responsibility. (#2)
• MergeResult now throws ArgumentError (not just assert) when invariants are violated, including the confidence-range bypass via the unvalidated PositionConfidence(double) primary constructor. Asserts strip in release; this guards engine output that flows into consumer caches. (#10)

Changed

• SDK constraint relaxed from sdk: ^3.8.1 to sdk: ^3.3.0 (extension types shipped in Dart 3.3 — the only modern feature this package uses). flutter constraint pinned to >=3.19.0 (the Flutter that bundled Dart 3.3). flutter_lints dev-dep pinned to ^5.0.0 to keep dev-deps SDK floor consistent with the package SDK floor. (#3)
• DriftTracker rolling windows switched from List (O(N) removeAt(0)) to dart:collection's Queue (O(1) removeFirst). Type now signals FIFO ring-buffer intent at the declaration site. (#4)
• DefaultTrackedBlock constructor throws ArgumentError (not just asserts) when the containerId / isInnerScrollerChild invariant is violated — the reference implementation is state-owning, asserts strip in release. (#5)

Fixed

• SpaceKey.regionIndex returns 0 as a safe fallback instead of throwing FormatException on malformed keys (forward-compat for externally- constructed or future-format-extension keys). (#1)

Internal

• New test files: test/space_key_test.dart, test/confidence_types_test.dart, test/merge_result_test.dart, test/default_tracked_block_test.dart. Test count: 207 (was 180 in v0.1.0).

0.1.0

Initial release.

Core

• StabilizationEngine — SAR merge, intra-batch dedup, contradiction detection
• DriftTracker — regional drift correction with submap isolation
• SpatialBlockIndex — grid-cell spatial index for O(cells) overlap queries
• OverlapResolver — spatial NMS with language-aware thresholds
• BlockKeyGenerator — position+text dedup keys with fuzzy neighbor matching
• BlockClassifierService — OCR group classification (fixed/sticky/carousel/IC/normal)

Types

• TrackedBlock<T> / ObservableBlock<P> — block identity interfaces
• AbsoluteRect — zero-cost coordinate-space safety (extension type)
• SpaceKey, ContainerId, ScrollContext, StickyFallback — value types

Utilities

• TextDedupUtils — Levenshtein, Jaccard, CJK detection
• RobustStats — median, MAD, IQR
• IqrOutlier — Tukey fence outlier detection