M4: the assembler — assemble → model → parse (Increment 2)

SharedKernel contracts (so Assembler stays decoupled): IAgentRunContextProvider (agent +
task) and ISkillCatalog (skill prompts by key). Implemented by OrgBoard (AgentRunContextProvider)
and Skills (SkillCatalog).

Assembler:
- PromptAssembler builds house-style + identity + the agent's skill bodies + the task, and
  derives the primary action + risk from the agent's first skill. RAG/working-memory join at M6.
- AgentRunExecutor (real): resolve context + skills → assemble → resolve BYOK config (with
  fallback) → call IModelClient → parse into action + risk → capture all on the AgentRun.

Verified: build green; ArchitectureTests 8/8; IntegrationTests 29/29 — incl. the M4 acceptance:
assigning a Spec task to Aria (PO, gated, stub BYOK) yields a Completed run with the assembled
prompt (skill body + task title), action "write-spec", risk "Draft", and model output. Nothing
executes — the gate is M5.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/TeamUp.IntegrationTests/AgentRunQueueTests.cs

@@ -67,8 +67,10 @@ public sealed class AgentRunQueueTests(PostgresFixture postgres) : IClassFixture
             Assert.Null(await queue.ClaimNextAsync("test-worker"));
         }
 
+        // With no agent configured for the random seat, the run reaches a terminal Failed state
+        // (the full assemble→model→parse path is covered by AssemblerRunTests).
         var fetched = await client.GetFromJsonAsync<RunResponse>($"/api/assembler/runs/{run.Id}");
-        Assert.Equal("Completed", fetched!.Status);
-        Assert.Equal("pending", fetched.ActionType);
+        Assert.Equal("Failed", fetched!.Status);
+        Assert.Contains("not found", fetched.Error ?? string.Empty, StringComparison.OrdinalIgnoreCase);
     }
 }