PR-2 of the multi-workspace external-agent stack. PR-1 (#2739)
landed per-workspace auth + heartbeat + inbox. This PR threads
``source_workspace_id`` through the A2A client + tool surface so an
agent registered against multiple workspaces can list peers across
all of them and delegate from a specific source.
Changes
-------
* ``a2a_client``: ``discover_peer``, ``send_a2a_message``,
``get_peers_with_diagnostic``, and ``enrich_peer_metadata`` now
accept ``source_workspace_id``. Routing uses it for both the
X-Workspace-ID header and (transitively, via ``auth_headers(src)``)
the bearer token. Defaults to module-level WORKSPACE_ID for
back-compat.
* ``a2a_client._peer_to_source``: a new lock-free cache mapping each
discovered peer back to the source workspace whose registry
surfaced it. ``tool_list_peers`` populates the cache on every call;
``tool_delegate_task`` consults it for auto-routing.
* ``a2a_tools.tool_list_peers(source_workspace_id=None)``: when
multiple workspaces are registered (MOLECULE_WORKSPACES) and no
explicit source is passed, aggregates peers across every
registered workspace and tags each entry with ``via: <src[:8]>``.
Single-workspace mode is unchanged — no ``via:`` annotation, same
output shape.
* ``a2a_tools.tool_delegate_task`` and ``tool_delegate_task_async``
resolve source via ``source_workspace_id arg → _peer_to_source[target]
→ WORKSPACE_ID``. Agents almost never need to specify ``source_*``
explicitly — call ``list_peers`` first and the cache handles the
rest.
* ``tool_delegate_task_async`` idempotency key now includes the
source workspace, so the same task delegated from two registered
workspaces produces two distinct delegations (the right behavior
— one per tenant audit trail).
* ``platform_auth.list_registered_workspaces()``: new helper for the
tool layer to enumerate the multi-ws registry. Lock-free reads
matched by the existing single-writer-per-workspace contract from
PR-1.
* ``platform_auth.self_source_headers``: now passes ``workspace_id``
through to ``auth_headers`` — without this, a multi-workspace POST
source-tagged with ``X-Workspace-ID=ws_b`` was authenticating
with ws_a's token (or no token if MOLECULE_WORKSPACE_TOKEN unset).
Latent PR-1 bug exposed by the new tool surface.
* ``a2a_mcp_server`` tool dispatch passes ``source_workspace_id``
from the tool call arguments.
* ``platform_tools.registry``: add ``source_workspace_id`` to the
delegate_task, delegate_task_async, check_task_status, list_peers
input schemas with copy explaining when to use it (rarely — the
cache handles it).
Tests (15 new, all passing)
---------------------------
``test_a2a_multi_workspace.py``:
* TestDiscoverPeerSourceRouting (3): src arg drives header+token,
fallback to module ws when omitted, invalid target short-circuits
before any HTTP attempt.
* TestSendA2AMessageSourceRouting (1): X-Workspace-ID source header
+ Authorization bearer both come from the source arg via the
patched self_source_headers chain.
* TestGetPeersSourceRouting (1): URL path AND headers use the
source workspace id.
* TestToolListPeersAggregation (4): aggregates across multiple
registered workspaces, tags origin, leaves single-workspace path
unchanged, explicit src arg overrides aggregation, diagnostic
joining when every workspace returns empty.
* TestToolDelegateTaskAutoRouting (3): cache-driven auto-route,
explicit override beats cache, single-workspace fallback to
module WORKSPACE_ID.
* TestListRegisteredWorkspaces (3): registry enumeration helper.
Plus ``tests/snapshots/a2a_instructions_mcp.txt`` regenerated to
absorb the new ``source_workspace_id`` schema entries.
Back-compat
-----------
Every change defaults ``source_workspace_id=None``; legacy
single-workspace operators (no MOLECULE_WORKSPACES) see identical
behavior — same URLs, same headers, same tool output. The 24
PR-1 tests + 125 existing A2A tests all still pass.
Out of scope (PR-3)
-------------------
Memory namespacing per registered workspace lands after the new
memory system v2 PR (#2740) settles in production.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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