workflow-fix: staging probe per source-family+consumer

Overview / Motivation

Auto-filed by the workflow-fix-on-bug protocol from the 2026-07-18 /daily transcript problem sweep (c3-P5 + c3-P12). Route-2 filing.

Goal

Make the artifact-reuse (h)(iv) 1-file staging probe run PER reused source-family AND per staged consumer, not once globally per plan — so a second reused source-family or a second consumer re-reading the staged layout is probed before production.

Workflow gap

• Bug observed: TWO #1481 staged-layout crashes landed the same day — datagen_topup/ vs datagen/ 404 at 06:14, and a hub.stage_hub_prefix reread-layout crash at 20:45.
• Why it is a workflow gap: artifact-reuse.md (h)(iv) requirement (3) ("BEFORE any production run, a 1-file staging probe + consumer-open") is phrased around "the artifact's ENTRY file" — a single probe. When a plan reuses MULTIPLE source-families staged into MULTIPLE consumers, one global probe leaves the others unprobed, so a mismatch in a second family/consumer crashes at run time.
• Confidence (emitter): medium
• verified-at-filing: grep -cn 'per reused source-family\|per staged consumer\|per source-family' .claude/rules/artifact-reuse.md → 0 hits; the (h)(iv) requirement (3) span (line ~223) prescribes ONE "1-file staging probe + consumer-open" against "the artifact's ENTRY file", with no per-source-family / per-consumer multiplicity requirement (2026-07-19)

Proposed change (candidate diff sketch — refine in planning)

# artifact-reuse.md (h)(iv) requirement (3): make the probe multiplicity explicit —
+ Run the 1-file staging probe + consumer-open ONCE PER reused source-family
+ AND per staged consumer (each family's entry file staged through its real
+ staging path, each consumer's entry-point open/init run against its staged
+ root); a single global probe on one family/consumer does NOT satisfy this
+ leg when the plan stages ≥2 families or ≥2 consumers (#1481: two same-day
+ staged-layout crashes — datagen_topup vs datagen 404, and a stage_hub_prefix
+ reread crash).

Scope / surfaces

• Primary target: .claude/rules/artifact-reuse.md
• Amend (h)(iv) requirement (3); keep the existing pure-mapping-fn + fail-loud-entry-check + real-staging-path requirements intact.

Constraints / invariants

• Workflow-surface only. Do not weaken the "must exercise the real staging path" requirement — this only multiplies the probe across families/consumers.
• scripts/workflow_lint.py --check-asks passes.
• Recursion guard applies.

Provenance

• workflow_fix_target: .claude/rules/artifact-reuse.md
• fingerprint: 6e2e44e3a0c0

Surfaced problem (c3-P5 + c3-P12): two #1481 staged-layout crashes in one day that a single global (h)(iv) staging probe did not prevent.