Enable ASYNC Step input snapshots by default

[longquanzheng]

Summary

• Turn blobStore.asyncStepInputSnapshotsEnabled back on by default when Blob Store is enabled, so semantic history keeps successful ASYNC local Step method inputs.
• Keep disable as an optional cost optimization: omit the flag or set it to true for the default; set false to skip snapshot writes.
• Update Server docs, Dex Web unavailable copy, and tests so operators can opt out without changing the default.

Test plan

• make -C server unitTests
• Dex Web EventDetails vitest
• make docs-prose-check and cd docs && npm run check
• Temporal/Cadence web_api integ coverage for default-on and explicit-off snapshots (CI)

skill-dex-developer stays blocked until this change is in a published Dex release. SuperVerse should disable the flag in its own Dex Server configs.

Made with Cursor

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...ent/history/async_step_input_snapshot_populator.go	50.00%	0 Missing and 1 partial ⚠️

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