chore(release): v0.6.0 — Observability & Decorators (M6.4)

[danielPoloWork]

Summary

Close Milestone 6 → v0.6.0 — Observability & Decorators. Bump the version, roll the changelog, draft the release notes, and refresh the README and roadmap. No code behaviour changes — this is the milestone-closing release PR (ADR-0004 §2).

Motivation

ROADMAP §6.4 — the release item that seals Milestone 6 (the InstrumentedPool Decorator, the PoolObserver, and the zero-overhead verification landed in PRs #47–#49). Versioning and the agent-prepares / human-tags-and-publishes boundary follow ADR-0004 §2 and ADR-0008.

Changes

• version.hpp → MINOR=6 PATCH=0, PBR_MEMORY_POOL_VERSION_STRING = "0.6.0"; the pool_smoke version-check TEST_CASE asserts the new components.
• CHANGELOG.md — the Unreleased block (M6.1 Decorator, M6.2 Observer, M6.3 zero-overhead test) is rolled into a sealed ## [0.6.0] — 2026-06-14 block with a milestone headline; the footer link references are rewritten ([Unreleased] → compare/v0.6.0...HEAD, new [0.6.0]), and a fresh empty Unreleased is seeded.
• docs/releases/v0.6.0.md — human-prose release notes (Decorator, Observer, the memory_pool_growths accessor, the zero-overhead contract) for release.yml to use as the GitHub Release body.
• README.md — status badge (v0.5.0 dynamic growth → v0.6.0 observability), a new At a glance observability bullet, the status paragraph, and the milestone table (Milestone 6 → ✅ complete, Milestone 7 → ⏳ next).
• ROADMAP.md — §6.4 flipped to [x] with the inline summary; a new M6 Session Checkpoint entry (next session resumes at Milestone 7).

Design Patterns

• None new — this PR closes the milestone in which Decorator (ADR-0025) and Observer (ADR-0026) were adopted; both are already Implemented in the catalogue. With them, every pattern planned through Milestone 6 is realised.

Verification

• Builds cleanly (MSVC 19.51 locally; full matrix via CI)
• Unit tests pass — full suite 10/10; the version-check case asserts 0.6.0
• markdownlint clean on the edited content (the lone MD060 hit is a pre-existing, unedited repo-layout table flagged only by a newer local markdownlint than CI's pinned version)
• N/A — docs + version-bump release PR, no library code change

Documentation Impact

• README.md updated (badge, status, table, at-a-glance)
• ROADMAP.md checkbox flipped (§6.4) + Session Checkpoint
• ADR — none (release item; no design decision)
• docs/patterns/README.md — unchanged (patterns flipped in feat(pool): InstrumentedPool Decorator + ADR-0025 (M6.1) #47 / feat(pool): Observer for pool-lifecycle events + ADR-0026 (M6.2) #48)
• Spec — unchanged (observability is additive; no spec row maps to M6)
• CHANGELOG.md rolled into [0.6.0]

Maintainer follow-up (post-merge)

Per ADR-0008: after merging, the agent tags v0.6.0 from master and pushes it; release.yml builds the artifacts and drafts the GitHub Release from docs/releases/v0.6.0.md; the maintainer clicks Publish.

🤖 Generated with Claude Code