[tonypodero]

What changed

• When the data converter has no payload codec and no external storage, workflow activations and completions skip the payload passes that cannot change a payload, and skip resolving a serialization context per command. The check that rejects external storage references without storage configured (TMPRL1105) still runs on every activation.
• DataConverter._decode_payload_has_effect had no callers. It is now _has_codec_or_external_storage, and both the bridge and the workflow worker use it.

Why

Since 1.23 the payload passes in decode_activation / encode_completion run unconditionally (#1288, #1341). 1.25 split them into two passes per direction (#1394) and 1.35 into three (#1946). From 1.25, each visited payload sequence also asks the workflow instance for its serialization context (#1387). For a sandboxed workflow, each of those lookups is an exec into the sandbox. With the default converter, none of this work changes a payload.

We hit this after upgrading 1.22 → 1.35. Long-running workflows (3k–8k events) are rebuilt from history after each deploy, and those replays became 1.3–1.6× slower, which pushed the largest past the workflow task timeout. On three of our own histories (2.6k–7.4k events), this change brings replay time back to 1.22.0's, 25–38% less than on 1.35.0.

Replay of a synthetic history (activity + 5-minute timer in a loop, default converter, default sandbox), relative to 1.22.0. Median of 3 interleaved rounds × 5 replays; macOS arm64, Python 3.12, protobuf 5.29.6:

	3,305 events	7,705 events
1.35.0	1.56×	1.51×
1.35.0 + this change	1.12×	1.15×

Where the time went (1.35.0, 7,705-event history, 1,402 activations)

• Sandbox _run_code calls per replay: 1,406 on 1.24.0 (one activate per activation), 6,310 on 1.35.0. The extra calls are 4,203 get_serialization_context and 701 get_external_store_context.
• decode_activation / encode_completion alone, with the default converter, per call: 0.1 / 0.1 µs on 1.22.0 and 10.9 / 12.9 µs on 1.35.0.
• Replay vs 1.22.0 by version: 1.23 1.03–1.05×, 1.24 1.04–1.07×, 1.25 1.35–1.47×, 1.34 1.39–1.42×, 1.35 1.55–1.58×.

How it was tested

• New test test_command_context_resolved_only_with_codec_or_external_storage: a workflow without a codec makes no context lookups, and one with a codec still does. It fails on 1.35.0 (3 lookups) and passes with this change.
• No local Rust toolchain, so I applied the change to the 1.35.0 wheel (these three files match main apart from unrelated lines) and ran the 1.35.0 tests against it:
  • test_serialization_context.py, test_extstore.py and worker/test_extstore.py: 88 passed, the same as unpatched.
  • worker/test_workflow.py, worker/test_replayer.py, worker/test_activity.py, and test_serialization_context.py with the new test: 348 passed, 2 skipped, 0 failed.
• Not run locally: poe lint-types and the full poe test on main.

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