fix(hooks): a fold does not make the signal partial

[fajarhide]

The second half of #775. [Partial signal] says the pipeline recognised some of the output
and not all of it, which is a claim about the distiller, and it was being read off a route
computed from final_out after the ledger has folded it.

So a payload the distiller never touched could reach Soft on the strength of a fold and
collect a banner over an answer nothing was lost from.

Reproduced, after three earlier attempts failed. The failures were the useful part:
both my first fixtures folded the whole payload, which lands in Keep, so the banner
never fired. The condition needs a partial fold. Sixteen of forty lines seen earlier:

[OMNI: 16 lines already shown from tail -16 app.log, omni retrieve 5b3d90904b481957]
2026-09-04T10:16:00Z INFO  worker 16 finished batch 112 in 27ms
... 23 more lines, verbatim ...

[Partial signal]

The fold is announced and retrievable, the other 24 lines are present, and the reply calls
itself partial.

route is left exactly as it is: it describes the delivered reply, which is what the
accounting that reads it wants. Only the banner moves to the ratio it is a claim about.

The other door was checked rather than assumed. hooks::pipe runs its ledger at
pipe.rs:364, after the banner at :328, so its ratio is already the distiller's and it
never had this. That is written into the changelog so the next person does not go looking.

Verification: make ci green, smoke_test.sh 70/70, and the reproduction re-run against
the release binary, where the banner is gone and the fold survives. Break-tested: putting
the delivered route back fails the new test with the full reply printed.

Closes #775

Greptile Summary

This PR makes the post-tool partial-signal banner depend on the distiller’s pre-ledger compression ratio rather than the delivered reply’s post-fold ratio.

• Separates banner classification from ledger-fold routing.
• Adds a regression test for a partially folded 40-line response.
• Documents the corrected behavior and why the pipe path is unaffected.

Confidence Score: 5/5

The PR appears safe to merge, with no actionable correctness or security issues identified.

The banner now reflects the distiller’s own reduction rather than a later ledger fold, while the existing delivered-route, guardrail, recovery, and passthrough behavior remains intact.

Important Files Changed

Filename	Overview
src/hooks/post_tool.rs	Correctly derives the partial-signal decision from the distiller output while preserving delivered-route accounting and adds focused regression coverage.
changelog.d/775b.fixed.md	Accurately documents the false partial-signal condition, the fix, and the unaffected pipe path.

_{Reviews (1): Last reviewed commit: "docs(changelog): record the partial-sign..." | Re-trigger Greptile}