GA audit follow-ups: non-blocker High/Medium/Low findings (API/CLI/MCP/SDK/DX)

[cyj-git-0825]

Follow-up to the GA-readiness audit in #493. These are the High/Medium/Low findings that are not GA-critical blockers (no data-loss/security-boundary/breaking-contract issue) and were intentionally kept out of the focused blocker PRs. All are additive / non-breaking — safe to land before or after the v1 freeze. Verified on main @ b43bad44.

The two headline pre-GA items are tracked separately:

• createApiKey idempotency → draft PR fix(api): make createApiKey idempotent via Idempotency-Key #495.
• CLI listen --json --forward forward-drop → branch fix/cli-listen-json-forward-drop (in progress).

API

• Non-uniform filtering/sorting across collections. Rich on listMessages/listEvents; listAgents/listDomains/listWebhooks/listTemplates are cursor+limit only. Real large-tenant usability gap (add optional query params — additive).
• Enumerate 401/403/404 per authenticated operation (currently only the catch-all default); broaden explicit 400s.
• Location header on 202 send/reply/forward responses.
• Product decision: keep the custom error envelope or adopt literal RFC 7807 (application/problem+json + type/title) — document either way.

CLI

• listen --once --forward exits 0 even when the forward POST fails — a blocking harness can't detect delivery failure (set process.exitCode = ERROR).
• No automated coverage for the top-level error→exit-code mapping (main()'s catch is gated behind isTestImport) or the listen TIMEOUT(6)/premature-close→ERROR(1) paths — frozen-contract regression protection.

MCP

• Dead agentIds filter type in client.ts createWebhook/updateWebhook (wire field is agentEmails; masked by an as cast) — a future refactor populating it per the declared type would silently drop the filter. Retype to agentEmails.

SDK (Python)

• Webhook/WS TypeGuards don't narrow — event.data stays Any, so the Email*Data/Domain*Data TypedDicts are unreachable (TS narrows genuinely). Biggest cross-SDK inconsistency.
• AsyncE2AClient.listen() annotated -> Any vs -> WSStream in TS.
• Retry ignores an HTTP-date Retry-After (seconds-only); TS honors both.
• from_api_exception can leak raw response body/headers into .message when the envelope is unparseable and reason is empty; TS avoids this.
• Align bounce_type/source to Literal[...] (plain str today); type the sync facade (__getattr__ -> Any).

Webhooks

• Delivery record next_retry_at is not advanced as River reschedules (stays at the initial value while the real next attempt moves forward) — polling clients see a stale timestamp.

Repo / DX

• Add a .gitattributes pinning api/openapi.yaml and the generated SDK dirs to eol=lf. On Windows (core.autocrlf=true) the LF-committed golden files check out as CRLF, so spec-check/generate-sdk-check/TestSpecGoldenNoDrift false-fail locally and a contributor can accidentally commit CRLF. Pinning eol=lf hardens the "handler is the spec" gate off the CI-only Linux path.
• CLAUDE.md is stale on the module path — it says github.com/Mnexa-AI/e2a, but the Go module was renamed to github.com/tokencanopy/e2a (commit 4b4beea6). (GitHub org/remote is unchanged.)

Full re-test evidence: AgentDrive audits/e2a-ga/retest-latest-b43bad44.md (see the supplement comment on #493).