feat(python): read idempotency-key generation config from the IR

[devin-ai-integration]

Description

Linear ticket: Refs #17018

Switches the Python SDK generator from its own auto_generate_idempotency_key config flag to the centralized ir.sdkConfig.idempotencyKeyGeneration block published in IR SDK 67.11.0.

Runtime behavior is unchanged: eligible requests receive a UUIDv4 idempotency-key header, and a caller-supplied value takes precedence. Enablement, header name, and eligible HTTP methods now come from the IR rather than generator-specific config and hardcoded POST/PUT checks.

idempotency_key_generation = self._context.ir.sdk_config.idempotency_key_generation
enabled = idempotency_key_generation is not None and endpoint.method in idempotency_key_generation.methods

Changes Made

• Read the idempotency header name and eligible method set from sdkConfig.idempotencyKeyGeneration while preserving the existing UUIDv4 injection and caller-wins fallback.
• Removed the old per-generator config plumbing by rebuilding on current main; the CLI-only auto-generate-idempotency-key key now reaches the generator through the IR.
• Bumped the Python v1 and v2 IR SDK dependencies to 67.11.0 and reconciled both lockfiles.
• Brought in the seed-harness fallback for synthetic invocations that populate resolved config without raw.config, with unit coverage.
• Regenerated the idempotency-headers and exhaustive feature-on fixtures using the kebab-case CLI key, with canonical seed metadata.
• Added an unreleased feat changelog entry.
• Updated README.md generator (if applicable) — N/A

Testing

• Unit tests added/updated — Python v1 pytest + mypy, Python v2 Vitest, and @fern-api/api-workspace-commons Vitest pass.
• Manual testing completed — pnpm seed test --generator python-sdk --fixture idempotency-headers exhaustive:auto-generate-idempotency-key --local --skip-scripts passes 3/3.
• Generated SDK verification — mypy passes for all three outputs; each output's pytest suite passes 72 tests with 4 skipped.
• Formatting/linting — Biome, Prettier, Ruff, and Python pre-commit hooks pass.

The feature-on generated client contains:

"Idempotency-Key": str(idempotency_key) if idempotency_key is not None else str(uuid.uuid4()),

The no-config fixture contains no UUID injection. Held for external sign-off; do not merge yet.

Link to Devin session: https://app.devin.ai/sessions/e429bcae88c74ab28101b488416486f2
Requested by: @cadesark

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SDK Generation Benchmark Results

Comparing PR branch against median of 5 nightly run(s) on main (latest: 2026-07-13T05:08:13Z).

Full benchmark table (click to expand)

Generator	Spec	main (generator)	main (E2E)	PR (generator)	Delta
python-sdk	square	135s (n=5)	241s (n=5)	135s	+0s (+0.0%)

main (generator): generator-only time via --skip-scripts (includes Docker image build, container startup, IR parsing, and code generation — this is the same Docker-based flow customers use via fern generate). main (E2E): full customer-observable time including build/test scripts (nightly baseline, informational). Delta is computed against generator-only baseline.
⚠️ = generation exited with a non-zero exit code (timing may not reflect a successful run).
Baseline from nightly runs on main (latest: 2026-07-13T05:08:13Z). Trigger benchmark-baseline to refresh.
Last updated: 2026-07-13 23:37 UTC

[devin-ai-integration]

Runtime-tested the generated Python SDKs locally through httpx.MockTransport.

• Passed — caller-supplied Idempotency-Key: caller-123 wins.
• Passed — default DELETE request has no idempotency header.
• Passed — custom IR { headerName: "X-Custom-Idem", methods: [PATCH] } injects a valid UUIDv4 on PATCH only; POST/PUT receive no idempotency header.
• Passed — feature-off fixture has zero uuid.uuid4() calls.
• Passed — temporary custom SDK passes mypy across 142 source files; worktree restored clean.

Runtime evidence

Key generated source

# committed feature-on fixture
"Idempotency-Key": str(idempotency_key) if idempotency_key is not None else str(uuid.uuid4()),

# adversarial temporary config: header-name=X-Custom-Idem, methods=[PATCH]
"X-Custom-Idem": str(uuid.uuid4())

Test session: https://app.devin.ai/sessions/e429bcae88c74ab28101b488416486f2

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