docs(matrix): LAB-519 ts stampede/backpressure cells + LAB-427 staleness fix

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Companion to cachekit-io/cachekit-ts#77 (LAB-519) — merge after or with that PR.

• Stampede cell (TS): refresh-path-only → full. In-process cold-miss single-flight (always on) + LockableBackend wired into wrap()'s miss path via opt-in stampede.distributedLock.
• Backpressure cell (TS): stays ⚠️ refresh-cap-only, now explicitly recorded as a deliberate decision with rationale (note under the Reliability table): event-loop model, single-flight collapses the per-key herd, distinct-key floods bounded by backend timeouts + circuit breaker.
• Drive-by staleness fix (LAB-427): the TS Redis capability cells still claimed no locking/TTL, but RedisBackend implements LockableBackend, TTLBackend shipped in cachekit-ts#74. Cells and the coverage note now match the code.
• TS architecture notes: test count/coverage refreshed (567 tests, 94.79% statements, measured on the ts#77 branch).

Summary by CodeRabbit

• Documentation
  • Updated the SDK feature matrix with the latest “Last updated” information.
  • Refreshed TypeScript capability coverage for cache stampede prevention, distributed locking (now marked as opt-in), backpressure (“refresh cap only”), and TTL management.
  • Clarified Redis and CacheKit SaaS support details, including TTL inspect/refresh and distributed locking scope.
  • Synced TypeScript architecture notes and updated stated test/coverage figures.

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• sdk-feature-matrix.md

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Walkthrough

Updated the TypeScript SDK feature matrix to document Cloudflare Workers status, Redis and SaaS locking and TTL support, single-flight behaviour, backpressure decisions, cache stampede prevention, and revised coverage figures.

Changes

TypeScript SDK capability documentation

Layer / File(s)	Summary
Capability and reliability matrix sdk-feature-matrix.md	Updates the TypeScript status stamp and capability cells for Redis locking and TTL support, records the LAB-519 backpressure decision, and documents cold-miss single-flight with SWR version tokens.
Architecture notes and coverage sdk-feature-matrix.md	Describes always-on cold-miss single-flight, opt-in stampede.distributedLock support through Redis and SaaS backends, and revised test and coverage figures.

Estimated code review effort: 1 (Trivial) | ~5 minutes

Possibly related PRs

• cachekit-io/protocol#10: Updates overlapping TypeScript reliability and capability cells in the feature matrix.
• cachekit-io/protocol#23: Covers overlapping TypeScript distributed-locking and TTL capability documentation.
• cachekit-io/protocol#30: Updates the TypeScript Cloudflare Workers status documented in the feature matrix.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title matches the docs matrix update and highlights the main TypeScript stampede/backpressure and staleness changes.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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• Commit unit tests in branch lab-519-matrix-ts-stampede

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Actionable comments posted: 2

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@sdk-feature-matrix.md`:
- Line 9: Update the “Last updated” date in the feature matrix metadata to the
actual publication or merge date, ensuring it is not later than the current
review date of July 23, 2026. Preserve the existing LAB-519 and LAB-427 change
description.
- Line 239: Update the coverage figures in the architecture note to include
their provenance: identify the cachekit-ts#77 branch and add the measurement
date or commit identifier so the reported tests and statement coverage are
reproducible.

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• sdk-feature-matrix.md

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