[bokelley]

Problem

A seller that validates a whole create_media_buy / update_media_buy request finds several problems at once, but a decisioning platform can only report them by raising AdcpError, which carries one code, message and field. build_mcp_error_result and the A2A failed-task builder wrote errors: [<that one error>], even when the caller put the whole list in details["errors"] (the slot AdcpError's docstring named for multi-error preflight). The issue's repro printed 1 [None]. Sellers had to lift the list in a response enhancer themselves.

Change

• AdcpError(..., errors=[...]): entries are AdcpErrors, generated Error models, or wire mappings with a string code and message. The raised error still fills the envelope adcp_error, and every entry goes into the payload errors[]. An entry without recovery takes the raised error's. Entry details go through sanitize_error_details like to_wire(). A malformed entry raises at construction (TypeError / ValueError).
• AdcpError.from_errors([...]) builds the raise from the list, with the first entry filling adcp_error, so adcp_error == errors[0]. It returns a base AdcpError even when the first entry is a subclass.
• AdcpError.errors_to_wire() returns the payload list: every entry, or [to_wire()] when there is no list.
• The details["errors"] slot is lifted. When errors= is not passed and every details["errors"] entry is a mapping with a string code and message, those entries fill errors[]. Any other shape (strings, {"path", "msg"} dicts, an empty list) is left alone, as before. adcp_error.details is unchanged.
• build_mcp_error_result, the A2A executor's failed-task DataPart and translate_error(..., "a2a") write the whole list. A single-error raise still mirrors adcp_error into errors[] (Raised AdcpError only fills adcp_error, so storyboards that read errors[0] fail #1558/fix(server): mirror a raised AdcpError into the payload errors array #1592), so existing output is unchanged.
• Docs: a short "Rejecting a request with every problem" section in docs/handler-authoring.md.

raise AdcpError.from_errors([
    AdcpError("BUDGET_TOO_LOW", message="budget below minimum", recovery="correctable", field="packages[0].budget"),
    AdcpError("INVALID_REQUEST", message="end_time before start_time", recovery="correctable", field="end_time"),
])

Not covered: an async TaskHandoff failure still records one error through registry.fail(task_id, exc.to_wire()), so tasks/get and the failure webhook report errors: [adcp_error]. Carrying the list there means a task-registry storage change, so it's left as a follow-up.

Adopter note: this change is additive. A seller whose response enhancer already lifts details.errors into errors[] (as the Scope3 sales agent's project_wire_errors does) gets the list from the SDK now. An enhancer that replaces errors keeps working; one that appends would duplicate the entries and should be removed.

Tests

tests/test_adcp_error_multi.py (28 tests) covers:

• construction, from_errors with all three entry types, and the subclass entry;
• malformed entries, sanitization, and copies;
• the details["errors"] lift, including the shapes it must leave alone;
• the issue's repro through build_mcp_error_result;
• context echo and response enhancer;
• end to end through _register_tool;
• translate_error A2A data, and the A2A executor's failed task.

Locally: make lint and make typecheck-all pass. The targeted error suites (test_adcp_error_multi, test_mcp_structured_error, test_a2a_structured_error, test_translate, test_decisioning_types, 149 tests) pass. I stopped the full local run partway because the sandbox ran out of memory, so CI's matrix is the full-suite gate.

A matching non-breaking PR against main (SDK 9) follows.

Closes #1780

🤖 Generated with Claude Code

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Open workspace in Conductor

[aao-secretariat]

Ladon verdict: Approve

Approve — additive multi-error support on AdcpError, no blocking findings.

Checked: feat(decisioning): is the correct semver signal — no public export removed/renamed, no required↔optional flip, no response-shape break; buyers still deserialize errors[] as a list. _error_entry_to_wire sanitizes entry details and refuses malformed entries (TypeError/ValueError) consistent with to_wire. from_errors recovery-default propagation is consistent between the first computation and __init__ re-normalization. The details["errors"] auto-lift (types.py L174-187) is gated on well-formed string code+message entries and leaves other shapes alone; the documented behavior change is handled in the PR body. Both A2A failed-task and MCP paths route through _payload_errors, single-error still mirrors (#1558). tests/test_adcp_error_multi.py:462 reproduces the issue end-to-end through build_mcp_error_result; 28 tests cover construction, sanitization, both transports, and _register_tool.

high_risk is true (modified files under decisioning/** and server/**), but with zero medium-or-higher findings these modifications are presumed safe (rows 4-5 do not fire). No gated paths, no no-auto-approve team match, no prior decision. Falls through to row 9.