Round 26 - What Can the Watchers Ever Know? Minimum Observables for Detecting Omitted Change

For each omitted-change failure class, which changed and unchanged worlds remain observationally identical, and what minimum independently rooted observable or trust assumption separates them?

E26-A is exact only for its declared finite model: 2, 16, 58, and 128 worlds at fault budgets 0 through 3, respectively. Seven failure roots and eight observable types were enumerated, with eight executable tests passed. Root independence is an assumption. The proposed Observation Sufficiency Certificate (OSC) is research-only, not installed or production-validated. No production incident was sampled, no language model was benchmarked, and no new Encevra answer benchmark was run. E26-B and H26.1 to H26.7 are proposed. Architecture impact: None. Production impact: None. The automation brief named Round 11, but the inspected archive ended at Round 25, making Round 26 sequential.

• In the declared one-fault universe, SACP leaves eight opposite-target ambiguity pairs; adding one independently rooted external commitment reduces that count to zero. Under two faults, SACP plus external commitment leaves 26 pairs; adding an independently rooted behavior probe reduces that count to zero. These are exact finite-model counts, not prevalence-weighted rates.
• Against three failed roots, four genuinely independent target-sensitive roots identify the target in the declared model. If the witness shares the issuer root, no available set identifies change against three failed roots. Root independence is an assumption.

• E26-A Deterministic finite-model identifiability analysis Executed (diagnostic)
• E26-B Prospective fixed-budget observation-sufficiency shadow experiment Proposed

• H26.1 Under one injected silent-root fault, SACP plus one genuinely independent target channel has fewer harmful false-stability certificates than SACP at matched total cost.
• H26.2 Three root-disjoint target channels are sufficient against two modeled silent-root failures in the implementation.
• H26.3 Removing or falsifying root-lineage metadata increases false stability under common-origin witness failures.
• H26.4 Health-only checks improve abstention and reduce false certification for visible path failures but do not detect healthy-looking selective non-emission.
• H26.5 Additional LLM agents sharing the same evidence root do not match one independent external channel at equal inference and observation cost.
• H26.6 Ambiguity-directed probes reduce residual pair weight per observation unit relative to fixed and random probes.
• H26.7 OSC's safety gain is not fully explained by abstention.

Research-only proposal. OSC was not installed. No release gate, claim state, retention policy, or production behavior changed. Production impact: None.

• Does OSC reduce harmful false-stability certifications at fixed total cost with hidden independent adjudication in E26-B?

Builds on Round 25, Round 24, Round 10, Round 9. Continued in Round 29, Round 28, Round 27.