fix(collector): recognize fully clipped live-region text

[tom-sapletta-com]

A screen-reader live region using clip-path: inset(50%) produced false TW-TEXT-CLIPPED findings during the C2004 audit because DOM Range still returned text rectangles. The collector now recognizes provably empty percentage inset shapes on the element and its ancestors, retains node/style evidence, and excludes the unpainted content from visual checks. Focused content that remains fully clipped blocks audit completeness.

Partial and unsupported shapes retain existing detection. Sixteen real-browser regressions cover live regions, actual overflow, shadow hosts and focus reveal; the reporting test covers the blocking gap.

Validation: hosted CI passed all 334 unit and 105 browser tests without failures or skips, including 16 new rendered clipping regressions. Pinned Docs validation and JavaScript syntax checks passed. Required checks are unit and browser; merge is handled by the independent Validator.

Closes #11. Unblocks source-bound revalidation of maskservice/c2004 PLF-2556; this PR does not claim application deployment.

[ifuri-validator-agent]

Validator approval after policy checks for exact head f121b9a5444f575a3ed442cb5677bd792d802b4d.

Ticket: ticket-012
Correlation ID: local-semcod-testwins-pr-12-ticket-012
Model: gemini/gemini-3.8-flash
Reviewed diff chunks: 2
Advisory LLM verdict: REQUEST_CHANGES
Advisory summary: Reviewed all 2 diff chunk(s). The PR introduces detection for visually empty CSS clip-path insets to prevent false TW-TEXT-CLIPPED findings. However, testwins/collector.js contains a fatal runtime TypeError when evaluating elements with default or non-inset clip-path values (such as 'none'). | The changes properly account for fully clipped elements (such as clip-path: inset(50%)) across collector element capture, heuristic alignment, visual detector passes, and completeness reporting. Focused clipped controls are flagged as a blocking scope gap to prevent unobservable visual focus.
Advisory findings: In testwins/collector.js, const parts = match?.[1].split(/\s+round\s+/)[0].trim().split(/\s+/) || []; attempts to invoke .split(...) directly on match?.[1]. When match is null (e.g., when clipPath is 'none', which is the default for almost all elements), match?.[1] evaluates to undefined, throwing TypeError: Cannot read properties of undefined (reading 'split'). This should use optional chaining (e.g., match?.[1]?.split(...)) or verify match before accessing properties.
The LLM output above is advisory and was not used as the approval trust root.
Semantic review prerequisite: not_required; policy 676cb4516bbfed2a000e40b9b1b6e4a430ecc761ec546aeb53d721a1905cfdd7.

Actual PR impact radar

Exact range: 9bd5bc8e27329de7db3e405256eed90a0a7b7948...f121b9a5444f575a3ed442cb5677bd792d802b4d
Change digest: 3f6523052b337969c2dfca91e2aefcfa7c1d8f813dc28ec9658081fefe772645
Score: 76/100 (L), estimated 102 min, split recommended: true
Affected services/components: repository-wide/unclassified

Machine-readable radar JSONL and SVG

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Merge will be attempted after this approval when explicitly authorized. ## Decision record (recomputable)

DECISION D-012-8483
TICKET ticket-012
HEAD_SHA f121b9a5444f575a3ed442cb5677bd792d802b4d
CORRELATION_ID local-semcod-testwins-pr-12-ticket-012
ACTOR agent:ifuri-validator-agent[bot]
APPLIED_RULE P-CORE-015
INPUT author_login = "tom-sapletta-com"
INPUT observed_checks = ["docker=SKIPPING","browser=PASS","browser=PASS","unit=PASS","unit=PASS"]
INPUT required_checks = ["unit","browser"]
INPUT required_checks_source = "protected registry (env/request)"
INPUT reviewer_login = "ifuri-validator-agent[bot]"
INPUT semantic_review_assessment = {"schema":"subactor.validator/semantic-review-assessment/v1","subject":{"repository":"semcod/testwins","pull_request":12,"head_sha":"f121b9a5444f575a3ed442cb5677bd792d802b4d","base_sha":"9bd5bc8e27329de7db3e405256eed90a0a7b7948","diff_sha256":"ff34adc0afa68c05265d47d3a754c9cc8b433a2322c5a77e0010f75f49c3e40d"},"policy":{"policy_schema":"subactor.validator/semantic-review-policy/v1","policy_version":1,"policy_sha256":"676cb4516bbfed2a000e40b9b1b6e4a430ecc761ec546aeb53d721a1905cfdd7","required":false,"critical_paths":[],"observed_paths":[".gitignore","docs/information/ux-strategies.md","project/ticket-012/README.md","tests/test_css_clipping_browser.py","tests/test_fail_closed.py","testwins/collector.js","testwins/detectors.py","testwins/reporting.py"]},"grounding":"full-diff-not-per-finding-proof","execution_authority":false,"status":"not_required","reason":null,"review_sha256":null,"unresolved":[]}
INPUT superseded_checks = []
INPUT ticket_radar_receipt = {"schema":"subactor.ticket-radar/v1","base_sha":"9bd5bc8e27329de7db3e405256eed90a0a7b7948","head_sha":"f121b9a5444f575a3ed442cb5677bd792d802b4d","change_digest":"3f6523052b337969c2dfca91e2aefcfa7c1d8f813dc28ec9658081fefe772645","score":76,"complexity":"L","estimated_minutes":102,"split_recommended":true,"services":[],"authority":"ADVISORY","promotion":"FORBIDDEN"}
VERDICT APPROVE AUTHORITY DETERMINISTIC
REJECTED REQUEST_CHANGES BECAUSE NO_UNSAFE_CHANGE_REASON_FOUND
ADVISORY llm_verdict = "REQUEST_CHANGES" MODEL "gemini/gemini-3.8-flash"
ASSERT VERDICT_AUTHORITY != "ADVISORY"