fix(templates): register the local Agentex tracing processor so the developer UI traces tab shows spans

[michaelxu2288]

Problem

The README's quickstart ends with "Investigate your agent's behavior by opening the traces tab", but every agentex init framework template registers only SGPTracingProcessorConfig, which disables itself when SGP_API_KEY / SGP_ACCOUNT_ID are empty. No other code creates a tracing processor (TracingProcessorManager starts with an empty list), so the spans the unified harness derives are never written to the backend /spans API and the traces sidebar shows "No spans found for this task" for any locally scaffolded agent.

Repro: agentex init (Sync ACP + Claude Code, or any framework), run it against ./dev.sh, send a message, GET /spans?task_id=<task> -> [], backend log has no POST /spans.

Fix

Register AgentexTracingProcessorConfig() ahead of the SGP block in all 16 framework templates (sync / default / temporal x openai-agents, pydantic-ai, langgraph, claude-code, codex, plus the OpenAI local-sandbox variant). SGP registration is unchanged. Fixes a comment in sync-langgraph that claimed to register the Agentex processor while registering SGP. Adds a parametrized test in tests/lib/cli/test_init_templates.py asserting every framework template registers the local processor.

Verification

• tests/lib/cli/test_init_templates.py: 42 passed (26 existing + 16 new).
• All 19 templates rendered through create_project_structure and byte-compiled.
• Fresh agent scaffolded from the patched sync-claude-code template against a local backend: message -> POST /spans, GET /spans?task_id=... returns the message (AGENT_WORKFLOW) span. Same for a temporal-claude-code agent (Turn 1/2/3 spans via the worker). Without the change: 0 spans.

Follow-ups (not in this PR)

• 22 tutorial/demo files under examples/ register SGP only, and 00_sync/020_streaming (which the README tells users to copy) registers nothing; happy to mirror this change there.
• Alternative that fixes everything at once: have the SDK auto-register the Agentex processor when AGENTEX_BASE_URL is set (idempotent, env kill-switch). That changes runtime behaviour for existing agents, so I kept this PR template-only; maintainers' call.

https://claude.ai/code/session_01HCVKnA7LeJZ44nxZz1uzF3

Confidence Score: 5/5

The PR appears safe to merge under the review rubric because no new reportable findings or outstanding previous findings remain.

Summary

• Adds registration to synchronous, asynchronous, and Temporal framework templates.
• Skips registration when AGENTEX_BASE_URL is explicitly empty in the process environment.
• Adds parametrized coverage ensuring every concrete framework template contains the registration.
• Preserves the existing optional SGP tracing setup.

Diagram

%%{init: {'theme': 'neutral'}}%%
flowchart LR
    H[Unified harness] --> S[Derived business spans]
    S --> M[Tracing processor manager]
    M -->|AgentexTracingProcessorConfig| A[AgentEx spans API]
    M -->|SGPTracingProcessorConfig| G[SGP tracing backend]
    A --> U[Developer UI traces tab]

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