[kyle-sexton]

No related issue: follow-up to #6389, salvaged from #6352

Summary

#6389 made the /discovery:research single-source first-party content-claim exception vendor-neutral, but left the single-publisher rule as it was. A claim about what a vendor's own docs page says has one source whose pool is the vendor, so under main's wording it still reads as a single-publisher fact: the verifier fails row 4 when it lacks subject_pool, and the cap holds it at MEDIUM. #6352 carried the fix for that interaction; this PR ports only that part onto main's current wording.

Fix

• discipline.md: a flagged content claim's subject is the artifact, so it carries no subject_pool and the single-publisher cap does not apply; the single-publisher definition excludes it, and a claim carries single_source: or subject_pool:, never both. The exception's artifact list adds the publisher's own help text.
• agents/research-verifier.md: row 4 exempts a flagged content claim from the cap, and a claim carrying both keys fails row 4.
• artifact-shape.md: omit subject_pool on a HIGH (single source) content claim.
• gotchas.md: the repost trap names a first-party content claim, not a single-publisher claim.
• evals.json: eval 33's expected output says "first-party file"; new eval 34 covers a non-Anthropic first-party content claim.
• contract.test.sh: four assertions for the above, plus an absence check for "what a named Anthropic page/file".
• discovery 0.28.9 -> 0.28.10 with one CHANGELOG line.

Verification

• bash plugins/discovery/scripts/contract.test.sh: all contract assertions passed, including the five new ones.
• bash scripts/validate-plugins.sh --only discovery: all plugin manifests and the catalog validated.

Related

• fix(discovery): let Gap claims keep their primary and make the single-source exception vendor-neutral #6389 (landed the vendor-neutral wording, discovery 0.28.9)
• feat(discovery): accept any publisher's own artifact as a single-source content claim #6352 (superseded draft this is salvaged from; closed in favor of this PR)

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-05T02:27:57.236944Z	50c29f7	Draft marked ready

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