fix(runner): restore acp backend MCP tools as fallback when sidecar is absent

[markturansky]

Summary

• PR feat(runner): dynamic credential-aware MCP server configuration #1593 removed the acp backend MCP server (9 session management tools: acp_list_sessions, acp_get_session, acp_create_session, acp_stop_session, acp_send_message, acp_get_session_status, acp_restart_session, acp_list_workflows, acp_get_api_reference) when adding dynamic credential-aware MCP servers
• The ambient MCP sidecar only provides equivalents for 5 of those 9 tools — stop_session, restart_session, list_workflows, and get_api_reference have no sidecar equivalent
• Sessions without the sidecar (e.g. older CPs, missing MCP_IMAGE config, or CP_TOKEN_URL/CPTokenPublicKey not configured) lost all session management tooling
• This re-registers the acp backend tools as a fallback when AMBIENT_MCP_URL is not set. When the sidecar IS present, its tools take precedence

Test plan

• 549/549 runner tests pass (1 pre-existing mlflow skip)
• 66/66 MCP + backend_tools tests pass
• Deploy to staging and verify acp_* tools appear when sidecar is absent
• Verify tools are NOT registered when sidecar IS present (no duplicates)

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features

  • Backend API tools are now automatically available in more deployment configurations, expanding functionality and flexibility.
  • Improved logging now surfaces discovered backend tools and their availability.

• Tests

  • End-to-end scheduled-session test now uses a stubbed workflow API to stabilize editing assertions and ensure OOTB workflow display and custom-field hiding.

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📥 Commits

Reviewing files that changed from the base of the PR and between 271a220 and 4b3c76a.

📒 Files selected for processing (1)

• e2e/cypress/e2e/scheduled-sessions.cy.ts

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📝 Walkthrough

Walkthrough

build_mcp_servers() now conditionally registers backend API tools as an "acp" MCP server when the ambient MCP sidecar URL (AMBIENT_MCP_URL) is not set, and logs discovered tool names and count. The E2E scheduled-sessions test now stubs the OOTB workflows API and waits for it before asserting UI state.

Changes

Backend MCP tool fallback

Layer / File(s)	Summary
Conditional backend MCP tool registration components/runners/ambient-runner/ambient_runner/bridges/claude/mcp.py	Import create_backend_mcp_tools and, when AMBIENT_MCP_URL is empty, build and register backend API tools under the acp MCP server name; log the number and names of discovered tools.
E2E: stub OOTB workflows in edit test e2e/cypress/e2e/scheduled-sessions.cy.ts	Add cy.intercept for /api/workflows/ootb*, alias @ootbWorkflows, visit the edit page and wait for @ootbWorkflows before asserting the workflow select and custom fields visibility.

Possibly related PRs

• ambient-code/platform#1006: Touches the same build_mcp_servers() path and updates ACP tool names/logging.
• ambient-code/platform#1593: Modified build_mcp_servers() ACP wiring previously; this PR reintroduces conditional ACP registration when sidecar is absent.

🚥 Pre-merge checks | ✅ 8

✅ Passed checks (8 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	Title follows Conventional Commits format (fix(runner): ...) and clearly describes the main change: restoring acp backend MCP tools as a fallback mechanism when the sidecar is absent.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Performance And Algorithmic Complexity	✅ Passed	Changes add conditional backend tool initialization (O(1) check, single bounded list of 9 tools) and test stubbing—no N+1, loops, unbounded growth, or expensive operations detected.
Security And Secret Handling	✅ Passed	No blocking security violations: no plaintext secrets, proper Bearer token auth, mock test data appropriate, no injection vulnerabilities or data leakage found.
Kubernetes Resource Safety	✅ Passed	PR contains only Python application logic and Cypress test changes; no Kubernetes manifests, RBAC policies, or resource definitions are modified.

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• Commit unit tests in branch fix/restore-acp-backend-tools

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• Commit simplified code in branch fix/restore-acp-backend-tools

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[mergify]

Merge Queue Status

• ✅ Entered queue — 2026-05-27 21:11 UTC · Rule: default
• ✅ Checks skipped · PR is already up-to-date
• ✅ Merged — 2026-05-27 21:12 UTC · at 4b3c76a185c66d6a79c95f02e7451bcf0a15768a · squash

This pull request spent 1 minute 4 seconds in the queue, including 10 seconds running CI.

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