refactor(tracing)!: drop the Agentex span processor and own the Span model in lib

[mohammadatallah-scale]

Important

Pending Mohammad's self-review. This note is removed by a human, not automation.

The problem. The Agentex server is retiring its Postgres spans API (scaleapi/scale-agentex#430). The SDK still ships the processor that writes to it and two trace helpers that read it back. The in-memory span handed to processors is that API's generated model, so it vanishes when the spec drops the routes.

The fix. This is a breaking change for the two removed surfaces.

• Span model: now lives in the library's tracing types and stays exported from the core tracing package, import it from there.
• Agentex processor: removed with its config type and the two read helpers. An unknown processor type now fails at registration naming the replacement.
• Generated files: untouched, Stainless removes the spans resource once the server spec merges. Land this first so the next branch keeps importing.

Test plan

• gap: not run against a generation without the generated span type, since that generation only exists after the server change merges. The compat suite still pins the current server spec.

Confidence Score: 5/5

The changes since the previous review appear safe to merge, with no new actionable failures identified.

Summary

• Exports the new library-owned Span throughout tracing, ADK, Temporal, examples, and tests.
• Removes the Agentex tracing processor, its configuration type, and span retrieval helpers.
• Rejects unsupported processor configurations with migration guidance toward SGP.
• Makes processor configuration locking reentrant and adds compatibility and registration tests.

Diagram

%%{init: {'theme': 'neutral'}}%%
flowchart LR
    Caller[Tracing caller] --> Tracer[Tracer / AsyncTracer]
    Tracer --> Trace[Trace / AsyncTrace]
    Trace --> Span[Library-owned Span]
    Span --> Manager[TracingProcessorManager]
    Manager --> SGP[SGP tracing processor]
    SGP --> Backend[SGP backend]

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_{Reviews (2) · Last reviewed commit: "fix(tracing): keep extra span keys, make..."}

[mohammadatallah-scale]

P2 CHANGELOG.md - the hand-maintained Unreleased breaking-changes block has no entry for the removed processor, config type and read helpers, or for the span model moving.
P2 tests/lib/core/tracing/test_tracing_processor_manager.py - only the rejection branch is covered, nothing drives an SGP config through the new guard and checks one sync and one async processor register.
P3 src/agentex/lib/types/tracing.py:22 - to_dict() / to_json() now return the full JSON-mode dump and model_construct no longer coerces datetimes, unlike the generated base. No caller in this repo, so a changelog line rather than a shim.
P3 trace.py:221,358 and span_error.py:14, sgp_tracing_processor.py:75 - prose still says these wrap the Agentex API or serialize through the Agentex processor.
P3 trace.py:239 - client is stored and never read now, and adk/_modules/tracing.py:173 still builds an httpx client per event loop only to pass it in.
P3 trace.py:327,482 - three blank lines left where the methods were removed.

[mohammadatallah-scale]

Landed in 62b97be: changelog entry under the Unreleased breaking changes, SGP happy-path and batch-registration tests, the stale prose, the optional client (the ADK module no longer builds an httpx client per event loop) and the blank lines. Left as documented rather than shimmed: the generated base's to_dict / to_json defaults and model_construct coercion, named in the changelog entry.