[casoon]

Partial work on the 2.0 foundation issues. None of the issues is closed by this PR; each keeps its open acceptance items.

#791 First-N selection

• summary.score_spread (min, median, max, std dev, five worst pages) and summary.selection_profile (page types, languages, unknowns counted).
• Representativeness claim removed from CLAUDE.md.
• Open: stratified selection, repeated performance runs.

#778 Coverage and completeness

• PDF principle coverage derived from executed rules, like the JSON; empty run is no longer 100 %.
• audit_scope.requested_rules: a requested shared rule without outcome fails validation.
• Execution-state matrix tests; an errored rule is counted once.
• Open: outcomes for tree/page/frame rules, per viewport and state.

#787 Session and state

• --session isolated|shared (default isolated, one browser context per URL).
• audit_scope.measurement_profile (session policy, read-only, state-changing journeys, state id, storage-state digest and counts, never values).
• --storage-state FILE, --state-id.
• Open: SPA fixtures, snapshot link ([2.0][U25] Schichten, Persistenz und Reproduzierbarkeit sind noch nicht geschlossen #790), Studio needs the new PipelineConfig fields.

#790 Snapshot

• Content fingerprint over the full AX tree and page-describing SEO; fingerprint version in cache meta.
• detail.module_detail (full, omitted, not_restored).
• tests/architecture_test.rs: dependency-direction ratchet.
• Open: full snapshot replay, persisted rule/score/schema versions, validation path matrix, 2.0 migration path.

Not touched

#784: code side is already on main; the human-labelled reference set is missing.

Checks

cargo test (non-ignored), cargo clippy --all-features --all-targets -D warnings, and the ignored Chrome tests of session_policy_test. Not run: rule_contract_gate beyond cargo test, reference sites, release CI.