feat(decisioning): credential-leak guidance + write-only field strip on every echo path

[bokelley]

Parent: #452

JS source

.changeset/account-store-sync-governance.md, commit ebaa4b3a docs(server): ctx_metadata credential-leak guidance (6.7).

Defense-in-depth

Write-only credentials should be stripped at the wire-emit boundary so adopters can return loosely-typed rows or spread DB records without leaking credentials.

Specifically:

• governance_agents[i].authentication.credentials — strip on emit.
• billing_entity.bank — already handled by project_account_for_response.

Need the same projection treatment for governance_agents[i].authentication.

Plus: ctx_metadata credential-leak doc

Add explicit guidance to CLAUDE.md (or equivalent surface) that ctx_metadata MUST NOT contain credentials — it round-trips to the client.

Acceptance criteria

• governance_agents[i].authentication.credentials stripped on every emit path (resolve / list / sync_governance / upsert echo).
• Tests verify strip — including a record with credentials present in the input does not appear in the wire output.
• Doc updated with credential-leak guidance for ctx_metadata.

Note

Some of this overlaps with #456's sync_governance(ctx) work. This issue covers the broader "every echo path" sweep + the documentation deliverable.

[bokelley]

Triage

Classification: Feature request (security defense-in-depth)
Bucket(s): handlers, docs (neither label exists in this repo — gap noted)
Status: deferred

What the experts said:

• (no panel — pre-classification structural defer)

My take: This is Batch 3 of epic #452. #456 (Batch 1, currently open) already covers governance_agents[i].authentication.credentials strip on sync_governance emit in its acceptance criteria. #463 extends that sweep to all remaining echo paths (resolve / list / upsert) and adds ctx_metadata credential-leak guidance. Blocking on #456 as a fold candidate — the broader sweep and doc deliverable can be pulled forward into #456 before merge rather than waiting for a separate Batch 3 round-trip.

Blocked-on: #456 — resurfaces on merge

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