fix(storyboard-runner): preserve sample_request fields in enrichers (#1604)

[bokelley]

Summary

Issue #1604 — src/lib/testing/storyboard/request-builder.ts fixture-aware enrichers rebuilt their request body from scratch and silently dropped any top-level sample_request field outside an enumerated allowlist. The non-proposal create_media_buy path was the immediate trigger (proposal-mode storyboards lose proposal_id, total_budget, idempotency_key from the YAML before they reach the wire). PR #1603 patched the proposal-mode branch but didn't apply the structural fix to the rest of the enricher.

Audit

FIXTURE_AWARE_ENRICHERS is the only set where the bug manifests — these enrichers bypass the outer fixture overlay ({ ...enriched, ...fixture }) in enrichRequest. Non-fixture-aware enrichers don't drop fields because the outer merge re-applies the fixture.

Enricher	Status before	Action
create_media_buy (non-proposal)	Build-from-scratch, dropped fields	Fixed — spread sample_request then override
create_media_buy (proposal)	Already spread (PR #1603)	Hardened — envelope fields omitted from local spread so mustache tokens expand via outer merge
update_media_buy	Already spread (PR #1505)	Hardened — same envelope omission
get_media_buys	Already spread (PR #1487)	Hardened — same envelope omission
get_media_buy_delivery	Already spread (PR #1487)	Hardened — same envelope omission
comply_test_controller	Already spread (#1419)	Hardened — same envelope omission

Structural fix

Spread sample_request first (after $context injection), then layer the runner's substitutions (account, brand, normalised dates, packages with discovery-derived identifiers) on top. Envelope fields (context, ext, push_notification_config, idempotency_key) are deliberately omitted from the local spread and re-applied by the outer enrichRequest with runnerVars so mustache substitutions like {{runner.webhook_url:<step_id>}} expand correctly.

A new omitEnvelopeFields helper centralises the envelope-omission discipline and is applied uniformly across every fixture-aware enricher that spreads sample_request.

Regression test

test/lib/request-builder.test.js — new test preserves top-level sample_request fields the enricher does not normalise (#1604). Pins total_budget, buyer_ref, currency, reporting_webhook pass-through. Verified to fail when the fix is reverted (79/80 pass; the new test fails as expected).

Allowlist

test/examples/hello-seller-adapter-proposal-mode.test.js EXPECTED_FAILURES is already [] (cleared by PR #1603 ahead of this structural fix). No further change required.

Verification

• npm run format:check — clean
• npx tsc --noEmit — clean
• node --test test/examples/hello-seller-adapter-proposal-mode.test.js — 3/3 pass
• node --test test/lib/request-builder.test.js test/lib/storyboard-envelope-passthrough.test.js — 84/84 pass
• npm test — 8338 pass, 0 fail (3 skipped)

Refs

• fix(storyboard-runner): create_media_buy enricher drops proposal_id, total_budget, idempotency_key from sample_request #1604 (this issue)
• fix(adapter): hello_seller_adapter_proposal_mode create_media_buy fails schema validation against AdCP 3.0.7 #1600 (original misdiagnosis — closed)
• fix(storyboard): proposal-mode create_media_buy request shape (closes #1600) #1603 (proposal-mode branch fix — predecessor)
• fix(test): drop stale get_products_refine allowlist on proposal-mode adapter #1599 (interim allowlist mask — already cleared)
• feat(examples): add hello_seller_adapter_proposal_mode for sole-stateful exemption coverage (#1549) #1594 (proposal-mode adapter)
• chore(deps): bump AdCP 3.0.6 → 3.0.7 (closes #1586) #1595 (3.0.7 bump that exposed the cascade)
• adcp#4088 (upstream chaining fix)

Test plan

• New regression test fails when fix is reverted
• Proposal-mode adapter gate passes with empty allowlist
• Full test suite passes
• Format and tsc checks clean

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