release: AHP 0.5.1

[connor4312]

Release AHP 0.5.1

Coordinated release of the spec + all 5 clients at 0.5.1. Next development version is 0.5.2.

Two commits:

1. 1c9acf63 — release commit: date-stamps every ## [0.5.1] CHANGELOG heading, bumps every client manifest 0.5.0 → 0.5.1, refreshes lockfiles, regenerates release-metadata.json.
2. 345c10dd — post-release bump: PROTOCOL_VERSION → 0.5.2 in types/version/registry.ts, regenerates every client's Version.generated.* and release-metadata.json, reopens ## [Unreleased] (+ ## [0.5.2] — Unreleased placeholder in the spec CHANGELOG) in every CHANGELOG.

Note: the root spec CHANGELOG previously had both a ## [Unreleased] section and a ## [0.5.1] — Unreleased placeholder with content split across them (the two most recent PRs — cursor pagination and lazy chat turn paging — mistakenly appended to ## [Unreleased] instead of the ## [0.5.1] placeholder). Since PROTOCOL_VERSION/SUPPORTED_PROTOCOL_VERSIONS were already 0.5.1-only, all of that content genuinely belongs to this release, so it was merged into the single dated ## [0.5.1] — 2026-07-02 section.

Use "Merge" (not squash) when merging this PR — the six release tags below must point at commit 1's SHA, and a squash merge would collapse both commits and break the PROTOCOL_VERSION tag-validation check in every publish workflow.

After merge — push the six tags

RELEASE_SHA=1c9acf632832bd517294299012b28f2ed133eef9
git fetch origin
git tag spec/v0.5.1        $RELEASE_SHA
git tag rust/v0.5.1        $RELEASE_SHA
git tag kotlin/v0.5.1      $RELEASE_SHA
git tag typescript/v0.5.1  $RELEASE_SHA
git tag v0.5.1             $RELEASE_SHA   # Swift — bare per RELEASING.md
git tag clients/go/v0.5.1  $RELEASE_SHA
git push origin \
  spec/v0.5.1 rust/v0.5.1 kotlin/v0.5.1 \
  typescript/v0.5.1 v0.5.1 clients/go/v0.5.1

Publish targets

Tag	Trigger	Publishes to
spec/v0.5.1	GitHub Actions Publish Spec	GitHub Release (schema assets)
rust/v0.5.1	GitHub Actions Publish Rust Crates	crates.io (ahp-types, ahp, ahp-ws)
v0.5.1	GitHub Actions Publish Swift Package	SwiftPM (tag-resolved)
clients/go/v0.5.1	GitHub Actions Publish Go Module	Go module proxy (tag-resolved)
kotlin/v0.5.1	Azure DevOps clients/kotlin/pipeline.yml	Maven Central via ESRP
typescript/v0.5.1	Azure DevOps clients/typescript/pipeline.yml	npm via ESRP

Kotlin and TypeScript publish via Azure DevOps pipelines (vscode-engineering tenant), not GitHub Actions — confirm those runs separately.