assess-cost report mode — deploy/billing telemetry integration for deploy-match

[rucka]

Story Statement

As a team monitoring cost drift with /assess-cost $mode: report
I want the panel's deploy-match dimension to actually resolve a merge to its deployment and to the observed cost movement
So that predicted-vs-real cost monitoring is corroborated by billing reality, not only by diff signals

Epic Context

Parent Epic: #208 (Unified classification & assessments → tags)
Status: Todo
Priority: P2 (Could-Have)

Problem

assess-cost report mode (#281, PR #388) declares a deploy-match dimension: with deploy/billing telemetry declared it should match a merged PR to its deployment and record the observed cost movement. As shipped in #281 only the degraded branch is executable — every project reports not available, because:

• no in-tree integration resolves a merge commit → deployment;
• no in-tree integration queries a per-service billing metric;
• no project declares the ## Cost & Billing Telemetry section the skill looks for.

#281's spec therefore names the declaration and the definition of "observed cost movement" as a contract and marks the matched path deferred, pointing here. Review finding on PR #388 (Minor): the positive path otherwise reads as a promise the spec cannot deliver.

Likely In Scope

• The ## Cost & Billing Telemetry declaration in infrastructure.md (shape + example), with assess-infrastructure/bootstrap awareness
• Merge → deployment resolution for at least one deploy source (e.g. GitHub deployments / releases)
• One billing-metric provider (AWS Cost Explorer first, per the KB's provider order), resolved through adoption like every other provider heuristic (R2.13 — no provider hardcoded in the skill)
• Definition of the comparison window (equal-length pre/post-deploy) and how the movement is rendered in the panel row
• Updating assess-cost Step 9.2 to drop the "deferred" note once the matched path is real

Likely Out of Scope

• Changing the cost class / signal catalog (quality-model §3.3, cost-assessment.md)
• Cost alerting or budget enforcement (report mode never blocks)
• The panel convention itself (working-area.md, ADL 2026-07-28)

Acceptance Criteria (draft)

• With a complete ## Cost & Billing Telemetry declaration, a merged PR's panel row carries a matched deployment and an observed cost movement
• With the declaration absent or incomplete, the row still reads not available — never a fabricated or inferred match
• Adding a second billing provider touches adoption/KB only, never the skill (R2.13)
• Conformance guard asserts both branches on the skill spec

Notes

Raised as a review finding on PR #388 (round 2). #281 stays scoped to the diff-signal side of monitoring.