flowtest: a var seeded from one case's `secrets:` prints in full for every other case

Problem

withheldMaterial (pkg/flowstate/v1/flowtest/vars.go:1799) deliberately skips a literal seed — a var whose value is a plain string that a secrets: entry names:

A literal seed: the secrets: entry naming it already carries its plaintext into the case that declared it, and this is the one place widening would reach a file that states no expression.

That justification assumes the seed's material only reaches the case that declared the secret. Substitution makes it false: any case may put ${vars.token} in any fixture position, and a case's posture is built from its own secrets: plus the withheld set — which the seed is excluded from.

Two reachable routes, both confirmed by execution (flowstate-reviewer, reviewing picatz/flowstate#2040):

Cross-case. tests[0] declares secrets: {env:VENDOR_TOKEN: ${vars.token}}; tests[1] declares no secrets and scripts signals[0].name: ${vars.token}:

test "signals": signals[0].name "sk-live-crosstest-1234" matches no gate…

Table row with its own secrets. mergeRow (pkg/flowstate/v1/flowtest/table.go:184) does if len(merged.Secrets) == 0 { merged.Secrets = entry.Secrets } — replace, not merge — so a row declaring any secrets of its own loses the entry's from its posture:

test "entry/row": signals[0].name "sk-live-rowown-1234" matches no gate…

Scope

• Pre-existing, and symmetric. flow test leaks both identically — caseError (run.go) renders the same sentence under the same posture — so this is not specific to the flow validate surface picatz/flowstate#2040 closes, and that PR is not the regressor. Confirmed on both surfaces.
• Material is a fixture value rather than a production secret, which is the same standing every other flowtest containment finding has.

Acceptance criteria

• A var named by any case's secrets: is withheld from every case's renderings in that file, or the literal-seed exclusion is replaced by something that does not assume one reader.
• A cases: row that declares its own secrets: still withholds the entry's material.
• Cases for both routes, on flow test and flow validate, since the posture is shared.

Two candidate shapes

1. Drop the literal-seed exclusion and let a seed join withheldVars like any other tainted var. Simplest, and widens what is withheld for files that state no expression — which is what the current comment says it was avoiding.
2. Make the posture file-wide for seeds: keep the exclusion, but add every case's secrets: plaintext to every case's posture. Narrower, and closer to what the material actually is — a value the file holds, not the case.

mergeRow's Secrets replace-not-merge wants deciding either way: a row overriding one entry is arguably not asking to drop the rest.

Related

• picatz/flowstate#2040 — routes flow validate's signal-name refusal through the redaction seam, adds the %q-escaped spelling and sensitive: input values to the posture, and documents this surface in the containment table. It does not touch the seed rule.

Start with withheldMaterial in pkg/flowstate/v1/flowtest/vars.go:1799, then inspect mergeRow in pkg/flowstate/v1/flowtest/table.go:184 and caseError in run.go to trace the shared posture and rendering paths. Reproduce both cross-case and row-specific-secret routes on flow test and flow validate. Done means every case withholds material named by any case's secrets, including entry material when a row declares its own secrets.