Fix historical sliding window semantics

[argahsuknesib]

Summary

Aligns Janus historical sliding-window execution with the Janus-QL specification.

Historical sliding windows now resolve as:

[T - OFFSET, T - OFFSET + RANGE)

instead of:

[T - OFFSET - RANGE, T - OFFSET)

Changes

• update historical sliding-bound resolution
• use checked arithmetic for temporal bounds
• preserve RANGE <= OFFSET validation
• preserve fixed historical-window behavior
• align historical executor and storage access paths
• align materialized-subquery, baseline, API, and benchmark paths
• update documentation and comments
• update public-spec, parser, API, executor, and storage tests
• add explicit half-open interval and boundary tests

Semantics

At evaluation instant T:

start = T - OFFSET
end   = T - OFFSET + RANGE

Therefore:

HistoricalSliding(T) =
[T - OFFSET, T - OFFSET + RANGE)

RANGE <= OFFSET ensures that the historical interval does not extend beyond T.

Verification

The following checks pass:

cargo fmt --check
cargo test
cargo check --benches
cargo clippy --all-targets --all-features -- -D warnings

[Copilot]

🔵 Needs a closer look

It changes core historical query semantics across parsing, execution, and storage boundary behavior, which is high-impact and warrants final human verification despite strong test updates.

Pull request overview

Updates Janus historical sliding-window execution to match the Janus-QL spec by resolving sliding historical bounds as a half-open interval anchored at T - OFFSET, and propagates that semantic through the executor, storage queries, API/baseline paths, docs, benchmarks, and tests.

Changes:

• Reworks historical sliding bound resolution to [T - OFFSET, T - OFFSET + RANGE) using checked arithmetic and keeps RANGE <= OFFSET validation.
• Introduces half-open query adapters (query_half_open / query_rdf_half_open) and updates historical sliding executors/operators to use them while preserving inclusive fixed-window behavior.
• Hardens storage durability and startup behavior around dictionary persistence (fail open when persisted segments exist but dictionary is missing/corrupt) and improves segment recovery metadata handling.

File summaries

File	Description
tests/segmented_storage_regression_test.rs	Adds regression coverage for failing to open persisted segments without a valid dictionary.
tests/segmented_storage_error_test.rs	Ensures synchronous flush failures (dictionary persistence) don’t commit segments and preserve in-memory query visibility.
tests/public_spec_behavior_test.rs	Updates spec-facing tests and expected messaging to reflect the new sliding historical semantics.
tests/janusql_parser_test.rs	Aligns parser error expectation strings with updated validation messaging.
tests/janus_api_integration_test.rs	Aligns API registration validation test expectations with updated historical sliding error messaging.
tests/historical_window_bounds_test.rs	Expands historical bound tests, including boundary/half-open query behavior against storage.
tests/historical_sliding_window_test.rs	Updates test comments to reflect half-open interval semantics.
src/stream/operators/historical_sliding_window.rs	Uses resolve_historical_bounds + half-open storage querying for historical sliding iteration.
src/storage/segmented_storage/segment.rs	Makes dictionary durability precede segment commit, adds failed-flush restoration, and improves segment/index recovery metadata reading.
src/storage/segmented_storage/query.rs	Adds half-open query adapters while keeping the underlying inclusive query API for fixed ranges/point lookups.
src/storage/segmented_storage/mod.rs	Fails fast when persisted segments exist but the dictionary is missing or unreadable; adjusts flush() to rely on the new durability ordering.
src/storage/segmented_storage/background.rs	Ensures background flush persists dictionary before segment commit and reuses shared failed-flush restoration.
src/registry/baseline_registry.rs	Updates baseline test expectations to match shifted historical sliding window bounds.
src/parsing/janusql_parser/mod.rs	Updates historical sliding validation error message wording.
src/parsing/janusql_parser/ast.rs	Implements checked-arithmetic historical sliding bounds as [T - OFFSET, T - OFFSET + RANGE).
src/execution/historical_executor.rs	Aligns historical execution paths to use half-open queries for sliding windows and inclusive queries for fixed windows.
src/bin/hybrid_scaling_combined.rs	Updates benchmark/driver historical subquery path to use half-open RDF querying for sliding windows.
src/api/janus_api/tests.rs	Updates API tests to use half-open RDF queries for historical sliding windows.
src/api/janus_api/baseline.rs	Uses half-open executor path when baseline sources are historical sliding windows.
docs/WINDOW_TYPES_EXPLAINED.md	Updates documentation to describe the new half-open historical sliding window semantics.
docs/JANUSQL.md	Updates language spec documentation for historical sliding window bounds and rationale.
benches/historical_sliding.rs	Updates benchmark commentary to reflect the new covered scan range/window count under half-open semantics.

Review details

• Files reviewed: 22/22 changed files
• Comments generated: 0
• Review effort level: Lite

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