[tconley1428]

Add shared category-folder changelog tooling for SDK release adapters. The new changelog-tool CLI validates per-PR Markdown fragments, writes a dated release section and consumes its fragments, extracts dated release notes, and resolves Core commit ranges from parent-repository Git links.

The existing range-note CLI remains available. Historical traversal now follows fragments through migration and release assembly without duplicating notes. Fragments contain the entry body without a leading list marker; tooling adds one bullet per nonempty line, allowing multiple entries in a fragment. Each entry occupies one line because each nonempty line becomes a separate list item. Agent guidance asks for concise entries, ideally one or two sentences. Breaking changes always use :boom: Breaking Changes; empty releases are always allowed, and empty sections produce no notes. Shared tooling uses anyhow to preserve error context. SDK adapters update versions and lockfiles first, then invoke the shared tool with the release version and date; they retain commits and PR creation. Validation completes before changelog writes or fragment deletion. Rust's own contributor convention remains unchanged for this first adoption.

Validation: 23 crate tests, targeted Clippy with warnings denied, and nightly formatting passed. Tests exercise real temporary Git repositories, fragment layout, body preservation, release assembly, validation failures without changelog mutation, PR diffs, and nested Core revision selection. A disposable Python SDK checkout also exercised real lockfile updates, release commits, published-note extraction, duplicate rejection and empty-release preparation/extraction, and a subsequent release consuming a late fragment.

The tooling crate remains unpublished; no SDK package version bump is required.

Companion PRs:

• Python adoption: Migrate to category-folder changelog fragments sdk-python#1919
• Shared workflow: Add alternative shared changelog fragment workflow .github#22

[chris-olszewski]

Overall makes sense, all of my comments are non-blocking