🪲 [Fix]: Escaped YAML tags preserve their exact identity

[Marius Storhaug (MariusStorhaug)]

This draft is stacked on yaml-conversion-foundation / #37 and contains only the remaining representation, conformance-policy, corpus, and CI artifact remediation. The updated base now owns the tag URI decoder itself; this PR does not duplicate that parser implementation.

What changed

• Verifies YAML 1.2.2 tag URI decoding through the built module for %21, multibyte UTF-8 escapes, malformed/incomplete escapes, and invalid UTF-8.
• Preserves unknown local and global tags exactly in representation nodes/events while keeping public PowerShell value projection neutral.
• Removes unknown-tag event policy fallback. Event differences are failures.
• Restricts syntax/composition policy to 2JQS and X38W with reason RepresentationMappingKeyUniqueness; both inputs are syntactically recognized and their representation events pass before load/composition rejects non-unique keys.
• Restricts JSON projection policy to 565N (BinaryByteArrayProjection) and J7PZ (LegacyOrderedMapProjection). Exact value validators and mutation regressions prevent these case IDs from masking unrelated mismatches.
• Restores the official data-2022-01-17 archive, records source/data commits and SHA-256, and prevents ZIP EOL normalization.
• Makes artifact imports terminating and validates generated metadata, exact exports/FileList, no Desktop/.NET Framework/assemblies/DLLs, and a fresh Core 7.6+ import/round trip.

Base CI failures and fixes

• Conformance: the checked-in ZIP had been text-normalized/corrupted; it contained records but extracted no corpus files and no longer matched the expected hash. This PR restores the official 402-input archive (47C173AFFEB480517B30FB77DC8C76FD48609B9B65DD1C1D3D0D0BAEE48D6AA9) and explicitly unsets ZIP EOL handling.
• Packaging: Process-PSModule derives generated runtime metadata from source #Requires; the source manifest alone left the artifact at PowerShell 5.1 with Desktop compatibility. The updated base supplies one module-header requirement pair (7.6, Core), and this PR locks the generated artifact contract with terminating built-module tests.
• Built-module test routing: representation inspection now executes private helpers in module scope, so Linux/macOS/Windows artifact jobs cannot silently fall back to dot-sourced source.

Official corpus results

Latest official source release remains v2022-01-17 (45db50aecf9b1520f8258938c88f396e96f30831); data tag commit is 6e6c296ae9c9d2d5c4134b4b64d01b29ac19ff6f.

Surface	Pass	PolicyDifference	Fail	NotApplicable
Syntax and composition	400	2	0	0
Representation events	308	0	0	94
JSON projection	277	2	0	123
out.yaml projection	241	0	0	161
Emit and round trip	306	0	0	96

Validation

• Local PowerShell 7.6.4 / Core: full source Pester 158 passed, 0 failed, 2 artifact-gated skips (160 total).
• Built artifact: packaging + conformance 20 passed, 0 failed, 0 skipped; fresh runtime marker powershell-runtime=7.6.4;edition=Core.
• Complete artifact-backed 402-input corpus: exact totals above; no unexplained failures.
• PSScriptAnalyzer: 0 findings. Parse checks: 65 files, 0 errors.
• Generated docs/site: 3 command docs, 17 site files, Zensical 0.0.47.
• Manual Process-PSModule run 30038857884: success, including conformance and packaging on Windows, Linux, and macOS. All three packaging jobs reported actual runtime PowerShell 7.6.3 / Core.

Remaining limitations

• This remains a draft stacked PR and depends on Draft: repository-owned YAML processor (Core 7.6+ conformance zero-fail) #37 / yaml-conversion-foundation landing first.
• The workflow only attaches PR checks for PRs targeting main, so the stacked PR has no native check suite; the successful manual dispatch above validates the final head SHA.
• The two source-run skips are artifact-only gates and pass in the separate built-artifact run.
• Local Zensical reports the existing generated-site warning that README.md links to CONTRIBUTING.md, which is not copied into the generated site.
• Unknown application-tag semantics are intentionally discarded only during PowerShell value projection; their representation tags remain exact.

No issue is linked because this remediation was requested directly as follow-up work for #37.