fix(lifecycle): align SDK validation and hook coverage

[jianpingpei]

Summary

• Add a real execd-as-init container regression that holds preStart at a host-controlled barrier and verifies /ping availability, PID 1, entrypoint and periodic ordering, repeated periodic execution, and lifecycle transport isolation.
• Keep the 1–300 second hook timeout range authoritative in the Server by removing duplicate client-side range enforcement from the stable Python and Kotlin models.
• Add a lifecycle hook guide with an editable timing diagram and creation examples for the C#, Go, JavaScript, Kotlin, and Python SDKs.

Related to #1542. This follows #1587, #1588, and #1589. Docker provider support, PATCH, additional hooks, and runtime protocol changes remain out of scope.

Testing

• Not run (explain why)
• Unit tests
• Integration tests
• e2e / manual verification

Validated:

• cd sdks/sandbox/python && uv run ruff check && uv run pyright && uv run pytest tests/ -q (519 passed)
• cd sdks/sandbox/kotlin && ./gradlew spotlessCheck :sandbox:test --rerun-tasks
• cd docs && pnpm@9.15.0 run docs:build
• bash -n components/execd/tests/init_container.sh
• Current-source init-mode container regression: all four cases passed using the current execd, bootstrap.sh, and launcher; the unrelated eBPF image stage was excluded from the local test image
• DrawIO source validation and visual inspection at full and 50% scale
• git diff --check

Breaking Changes

• None
• Yes (describe impact and migration path)

Checklist

• Linked Issue or clearly described motivation
• Added/updated docs (if needed)
• Added/updated tests (if needed)
• Security impact considered
• Backward compatibility considered

[chatgpt-codex-connector]

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