Phase 003: remove the coding-agent and ekko-agent runtimes

Every chat session now runs through the Hermes bridge, so the three chat
chains become feature-equivalent instead of three partially-maintained
dispatch paths. Keeping the coding-agent and in-house agent runtimes alive
meant every bridge change had to be mirrored into two more runtimes that
had already drifted.

Historical rows are read, not migrated: sessions stored with the retired
source normalize to cli on load, workflow graphs naming the retired agents
keep loading and run on the bridge, and the visible-source check plus
SOURCE_LABELS still recognize the old value so those sessions stay listed.

The public surface follows the code: the OpenAPI generator and the MCP
chat-run tool schema drop the six retired entry fields so external callers
are not told about runtimes that no longer exist.

harness-check gains a RETIRED_RUNTIME scan so the residual check is a
mechanical gate instead of a manual grep, with the two surviving read-side
compat sites recorded with reasons.

Refs: docs/phases/phase_003.md

tests/server/workflow-manager.test.ts

@@ -61,31 +61,20 @@ describe('workflow manager', () => {
     expect(updates).toEqual([status])
   })
 
-  it('maps workflow node agents to the existing run backends', async () => {
+  it('routes every workflow node through the Hermes bridge', async () => {
     const { resolveWorkflowNodeRunTarget } = await import('../../packages/server/src/services/workflow-manager')
 
-    expect(resolveWorkflowNodeRunTarget('hermes')).toEqual({
+    const expected = {
       type: 'workflow',
       source: 'workflow',
       agent: 'hermes',
-    })
-    expect(resolveWorkflowNodeRunTarget('claude-code')).toEqual({
-      type: 'workflow',
-      source: 'workflow',
-      agent: 'claude',
-      codingAgentId: 'claude-code',
-    })
-    expect(resolveWorkflowNodeRunTarget('codex')).toEqual({
-      type: 'workflow',
-      source: 'workflow',
-      agent: 'codex',
-      codingAgentId: 'codex',
-    })
-    expect(resolveWorkflowNodeRunTarget('unknown')).toEqual({
-      type: 'workflow',
-      source: 'workflow',
-      agent: 'hermes',
-    })
+    }
+    expect(resolveWorkflowNodeRunTarget('hermes')).toEqual(expected)
+    // Workflow graphs saved before Phase 003 still name the removed coding
+    // agents; they must keep loading and run on the bridge.
+    expect(resolveWorkflowNodeRunTarget('claude-code')).toEqual(expected)
+    expect(resolveWorkflowNodeRunTarget('codex')).toEqual(expected)
+    expect(resolveWorkflowNodeRunTarget('unknown')).toEqual(expected)
   })
 
   it('requires workflow node approval only when explicitly enabled', async () => {