fix: never strip canonical AdCP request fields for partial-schema agents

[EmmaLouise2018]

Production symptom

The 3rd-party AdCP sales agent Open Ads (https://api.openads.ai/mcp) advertises a partial tool inputSchema via tools/list. Production stderr (last 3 days, agent "33"/Open Ads) showed the SDK stripping canonical request fields before the request ever left the client:

[AdCP] Stripping fields not declared in agent "..." schema for update_media_buy: creative_ids
[AdCP] Stripping fields not declared in agent "..." schema for sync_creatives: media_buy_id
[AdCP] Stripping fields not declared in agent "..." schema for get_media_buy_delivery: media_buy_id

This silently broke media-buy updates and delivery polling against any seller that under-declares its schema — including dropping the canonical-required media_buy_id on update_media_buy.

Root cause

SingleAgentClient.adaptRequest (the strip loop around src/lib/core/SingleAgentClient.ts:2154) kept a top-level field only when it was declaredFields.has(key) || envelopeFields.has(key) — i.e. it intersected the outgoing request with only the agent's self-declared (partial) schema plus ADCP_ENVELOPE_FIELDS. The strip fails open only when the cached schema has zero properties; a non-empty but partial schema fails closed, dropping legitimate canonical protocol fields the agent simply forgot to declare.

The fix

Union the keep-condition with the canonical AdCP request schema for the task, via the existing schemaAllowsTopLevelField helper in src/lib/validation/schema-loader.ts:

if (
  declaredFields.has(key) ||
  envelopeFields.has(key) ||
  schemaAllowsTopLevelField(taskType, key, this.resolvedAdcpVersion)
) {
  filtered[key] = value;
} else {
  schemaStripped.push(key);
}

A field is now preserved when it is declared by the agent schema, OR is a protocol envelope field, OR is a canonical top-level field for that task in the resolved AdCP version. Only fields unknown to both the agent schema and the canonical request schema are stripped (genuine junk / unknown vendor extensions).

Why it's safe

• Fail-open preserves. schemaAllowsTopLevelField returns true when no canonical schema is indexed for the tool (custom/unsynced tools), so the change is preserve-on-doubt — it never strips more than before.
• Junk still stripped. A field that is neither agent-declared nor canonical (e.g. totally_made_up_field) is still dropped and still logged via console.warn + the input_schema_field_stripped debug log.
• Envelope unaffected. ADCP_ENVELOPE_FIELDS membership is still honored.
• Mapping verified. taskType is the snake_case tool name (update_media_buy, get_media_buy_delivery, sync_creatives) — exactly the toolName key the loader looks up as ${toolName}::request in its fileIndex (same names used by existing schemaAllowsTopLevelField('sync_creatives', ...) callers and by TaskExecutor.validateRequest). The version arg is the raw this.resolvedAdcpVersion pin; the loader resolves the bundle key internally via ensureInit/resolveBundleKey, matching TaskExecutor.validateRequest(taskName, params, ..., this.config.adcpVersion). A runtime probe confirmed: for 3.1.0, media_buy_id/media_buy_ids/creative_ids → true (preserved); totally_made_up_field → false (stripped). A wrong mapping would have made the helper return true for everything (fail-open no-op); it does not.

Tests

test/lib/request-validation.test.js:

• Updated the existing partial-schema get_products test: brand is canonical for get_products, so it is now preserved (the old test encoded the buggy strip); a genuinely-unknown totally_made_up_field is the one asserted stripped.
• Added Open Ads regression cases for update_media_buy (canonical media_buy_id preserved), get_media_buy_delivery (canonical media_buy_ids preserved), and sync_creatives (canonical creative_ids preserved) — each against an agent whose cachedToolSchemas declares only a subset, asserting the canonical field survives adaptRequest while totally_made_up_field is still stripped.

Verification: npm run typecheck clean; npm run build:lib clean; targeted file 39/39 pass; full fast lib suite 9628 pass / 0 fail / 7 skipped; prettier --check clean on changed files. Changeset added (@adcp/sdk: patch).