Preserve execution cost when a completed render produces unchanged output

[irl-dan]

Observed need

During a manually interpreted observatory run, meaningful investigation and review sometimes concluded that the previously published account should remain unchanged. A no-change outcome still involved actual agent work. This prompted a review of how OpenProse receipts distinguish work avoided from work completed without a material output change.

This issue reports a specification inconsistency at fc2810e, not a reproduced bug in a deployed harness. Our application kept explicit no-change outcomes rather than using the mounted-runtime receipt protocol.

Conflicting instructions

• Reconciler memo/skip skips before spawning when the contract/input memo key is unchanged.
• VM harness seam associates zero cost with that pre-render skip.
• Filesystem canonicalization pass, however, runs after a candidate artifact exists and says that unchanged output fingerprints produce a skipped receipt with zero cost.
• Commit-and-sign repeats the post-render skipped outcome. The receipt definition describes cost as mechanical token attribution.

A changed input can legitimately trigger an expensive render whose material output remains identical. Following the filesystem instruction literally would erase that render's recorded cost and conflate it with a cache hit.

Minimal scenario

1. Existing output has fingerprint O1; previous input tuple is I1.
2. An input moves to I2, so a render is launched.
3. The host records nonzero model usage during that render.
4. The candidate's material fingerprint is still O1.
5. No downstream wake is appropriate, but reporting zero render usage is incorrect.

Requested clarification

Distinguish a pre-execution memo skip from an executed-but-unchanged result. Preserve observed usage and execution provenance after work has run; represent unavailable usage as unknown rather than zero. Retain the unchanged published version and avoid downstream propagation. Record the satisfied I2 tuple so the next identical wake can genuinely skip.

Choose whether this uses an existing status with an explicit reason/executed distinction or another representation; no new status or syntax is prescribed here. Keep publication/change detection independent of whether work happened.

Boundary and retestable acceptance

Align VM, filesystem and reconciler semantics; harness implementations remain outside this repository. Add a fixture with a fake renderer/canonicalizer and a nonzero usage report:

• unchanged input: renderer not called;
• changed input, same output: renderer called, usage retained, published version unchanged, no downstream wake;
• next wake with the same new input: renderer not called again;
• changed output: ordinary commit and propagation;
• unknown usage: not fabricated as zero.

A deterministic fixture would test accounting and propagation, not the quality of agent judgment. No hosted billing or pricing semantics are requested.