Harden pattern dispatch and error contracts for 3.1

[mxsm]

Summary

• route starts_with, ends_with, and contains through a private sealed pattern classifier
• retain StrPattern::as_str_pattern and its dispatch value as unchanged 3.1 compatibility surfaces
• add downstream-style contracts for char, &str, &String, constructor errors, substring errors, display, and source chaining
• document the exact pattern and error matrix in root API.md
• add a pinned API compatibility workflow that applies minor-release semver rules against origin/main
• correct stale packed-migration wording now that the stable immutable value has a safe 24-byte layout

Compatibility

• no existing public method, trait, enum variant, type alias, or return type is removed, renamed, deprecated, or changed
• cargo-semver-checks passed 196 checks against origin/main; no semver update is required
• targets CheetahString 3.1.0 with Rust 1.95 MSRV
• no files under docs/ or docs/rocketmq-doc are included

Verification

• format, clippy, all-feature and no-default test matrices
• 32 doctests, including the external sealed-trait compile-fail contract
• warning-free default/all-feature rustdoc with 100% public item and example coverage
• Rust 1.95 direct API test and packaged consumer matrix
• Miri core/API/basic/bytes suites
• all fuzz targets build on nightly
• cargo audit, actionlint, Python repository contracts, package content audit
• cargo-semver-checks minor-release comparison

Closes #150

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📥 Commits

Reviewing files that changed from the base of the PR and between 74c4293 and da5df60.

📒 Files selected for processing (9)

• .github/workflows/api-compatibility.yml
• API.md
• CHANGELOG.md
• README.md
• scripts/tests/test_repository_contracts.py
• src/cheetah_string/pattern.rs
• src/cheetah_string/query.rs
• src/error.rs
• tests/api_contract.rs

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[Copilot]

Pull request overview

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Hardens the internal pattern-dispatch implementation and codifies 3.1-compatible error/pattern contracts, including documentation and CI enforcement.

Changes:

• Route starts_with / ends_with / contains through a private classifier while keeping StrPattern::as_str_pattern + StrPatternImpl as compatibility shims.
• Add downstream-style contract tests for pattern dispatch and error signature/display/source behavior.
• Introduce API compatibility documentation and a GitHub Actions workflow that gates minor-release semver compatibility vs origin/main.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
tests/api_contract.rs	Adds integration tests that lock in downstream-callable compatibility surfaces and error contracts.
src/error.rs	Updates Error docs to clarify 3.1 compatibility and Utf8Error wrapping behavior.
src/cheetah_string/query.rs	Switches query methods to use the new private pattern classifier.
src/cheetah_string/pattern.rs	Introduces classifier enum + sealed classification method; keeps as_str_pattern/StrPatternImpl as a shim.
scripts/tests/test_repository_contracts.py	Enforces repository-level contracts around private dispatch and pinned semver workflow semantics.
README.md	Updates migration wording to reflect the safe 24-byte layout status.
CHANGELOG.md	Notes the dispatch hardening and compatibility workflow additions; updates migration wording.
API.md	Documents the exact pattern + error contract matrix and local reproduction steps.
.github/workflows/api-compatibility.yml	Adds a pinned workflow that runs cargo-semver-checks against origin/main under minor rules.

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