fix(xml): dispatch v2.6/v2.7 namespaces + default unknown to Max

[ottobolyos]

Summary

MTConnectVersion.GetByNamespace failed to recognize the v2.6 and v2.7 XML namespaces, resolving any such document to an empty Version (0.0) instead of the correct release. This patch adds the missing dispatch branches and changes the fallback for an unrecognized namespace to the latest supported release instead of an empty version.

Root cause

libraries/MTConnect.NET-XML/MTConnectVersion.cs:22-44 — the GetByNamespace(string ns) dispatch chain checked namespaces from Namespaces.Version25 downwards and then fell through to return new Version();. The Namespaces.Version26 / Namespaces.Version27 classes and the MTConnectVersions.Version26 / MTConnectVersions.Version27 constants already existed elsewhere in the codebase, but no branch matched them here — a pure dispatch omission, not a missing feature.

Effect: a document declaring urn:mtconnect.org:MTConnectStreams:2.7 (or :2.6) resolved to version 0.0, which downstream consumers would either reject as invalid or accept with the wrong version metadata attached.

Fix

• Added Namespaces.Version27.Match(ns) and Namespaces.Version26.Match(ns) branches at the top of the chain, ahead of Namespaces.Version25, so namespaces resolve highest-first (mirroring the existing ordering).
• Changed the fallback from return new Version(); to return MTConnectVersions.Max;, so an unrecognized namespace now defaults to the latest supported release rather than an empty version.

v2.8 namespace support is out of scope here — no Namespaces.Version28 exists yet, so no v2.8 branch was added.

Dime review cycle 1

Retroactive backfill (2026-08-20). The 6-agent Ultrareview cycle ran on this PR (verified on bluefin worktree .claude/pr229-verify at head 251f76b4; build rc=0, 0 warnings, 0 errors; 9-of-10 test projects passed — SHDR 63, Common 3987, XML 198, MqttRelay 35, JSON-cppagent 112, HTTP 363, Compliance 225, JSON 62, Integration 16 = 5,061 tests; Docs-Tests hit documented bluefin Playwright flake). Ledger reconstruction from commit history:

• [TEST] test-coverage-audit — every-kind + boundary + Get() surface pin for the dispatch chain (F-TEST-002..004) landed in test(xml): pin every kind + boundary + Get() surface for dispatch chain (b3dbaa4, 620e8010 reference).
• [FINDING] code-review — sibling bug (F-TEST-001) Assets arm missing from Namespaces.Version12.Match surfaced during the every-kind sweep; fixed atomically in fix(xml): include Assets arm in Namespaces.Version12.Match (5a150a3, 6c21771e reference).
• [FINDING:A05] security-audit HIGH (F-SEC-001) — Namespaces.Get(string) needed hardening against XXE and entity-expansion attacks; fixed atomically in fix(xml): harden Namespaces.Get(string) against XXE and entity expansion (13344d0, ebf0011e reference).
• [DOCS] documentation-audit (F-SIMP-003, F-CR-002, F-CR-004, F-CR-006) — Get/GetByNamespace summaries and InternalsVisibleTo annotation clarified in docs(xml): clarify Get/GetByNamespace docs; annotate InternalsVisibleTo (960fe8b, 251f76b4 reference).
• [FINDING] code-review F-CR-001 — fallback change to MTConnectVersions.Max: CLOSED with rationale — explicit design intent already stated in the original fix(xml) commit message and PR title.
• [FINDING:A08] security-audit F-SEC-002 — same fallback change: CLOSED with same rationale as F-CR-001.
• [IMPROVE] improvement F-IMP-001 — Trace.TraceWarning on unknown-namespace fallback: CLOSED with rationale — silent forward-compat is by design; the follow-up F-IMP-002 TryGetByNamespace surface is the cleaner escape hatch for strict-conformance callers.
• [TEST] test-coverage-audit F-TEST-005 — TDD ordering on the original fix commit: TRACKED — deferred to human reviewer (splitting a pushed head SHA would rewrite an already-flipped-to-draft PR; the 620e8010/6c21771e ordering demonstrates the correct pattern for the sibling bug).
• [DOCS] documentation-audit F-DOC-002 — docs/wire-formats/xml.md:117 stale "returns empty Version" for v1.9: TRACKED against docs(wire-formats): correct XML codec fall-through description #232 (needs re-verification to cover lines 3, 82, and 117).
• [DOCS] documentation-audit F-DOC-003 — docs/wire-formats/xml.md:3, :82 stale "up to v2.5" claim + Max annotation on v2.5 row: TRACKED against docs(wire-formats): correct XML codec fall-through description #232.
• [IMPROVE] improvement F-IMP-002 (TryGetByNamespace) / F-IMP-003 (data-driven dispatch) / [FINDING] code-review F-CR-005 (dictionary refactor): FOLLOW-UP issues suggested; out of PR scope.

(Zero unfixed findings — Ready-eligible.)

Depends on

• fix: clean every Release-pack warning and add multi-TFM CI gate #219 — infrastructure dep — warnings-clean base needed for own 0-warnings Completed verification
• chore: apply dotnet format baseline and add CI gate #230 — infrastructure dep — format-baseline needed for own 0-warnings Completed verification