fix(client): stop nested $transaction from mutating the caller's options object

[lazerg]

Problem

_transactionWithCallback writes newTxId into the options object the caller passed when the call is nested, then reads newTxId back off that same object on every call, top-level ones included. An application that keeps a shared options constant — const TX_OPTIONS = { timeout: 30_000, maxWait: 10_000 } — and passes it to a nested tx.$transaction(cb, TX_OPTIONS) once leaves that object permanently stamped with the outer transaction's id. Every later top-level prisma.$transaction(cb, TX_OPTIONS) in the process is then sent to the engine as a nested start against that id: it fails with P2028 if the outer transaction has committed, or silently opens as a savepoint inside another request's still-open transaction if it has not.

Change

The nested transaction id is no longer written into the caller's object. optionsWithDefaults derives newTxId from the itx scope context of the client the method was called on, so it is set only when the call is actually nested and a polluted options object can no longer make a root-client call join someone else's transaction.

Tests

Added sql: nested transaction does not mutate the options object to packages/client/tests/functional/interactive-transactions. It reuses one options object across a nested transaction and a later top-level one, asserting the object is unchanged and that both transactions committed. It fails on the current code (the object gains newTxId) and passes with the fix.

The full interactive-transactions suite passes on sqlite/better-sqlite3 (38 tests), as do the other transaction suites (47) and @prisma/client-engine-runtime (234).

Fixes #30367

Summary by CodeRabbit

• Bug Fixes

  • Improved nested transaction handling so shared transaction options remain unchanged.
  • Preserved reliable behavior for nested and top-level interactive transactions, including safe transaction identifier handling.

• Tests

  • Added coverage confirming transaction options can be reused safely across nested and subsequent transactions.
  • Verified that multiple transactions using the same options complete successfully and preserve all expected data.

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• packages/client/tests/functional/interactive-transactions/tests.ts

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📝 Walkthrough

Walkthrough

The runtime no longer writes newTxId to caller-provided options. It derives the identifier when constructing nested transaction defaults. A SQL functional test verifies option reuse across nested and later top-level transactions.

Changes

Interactive transaction options

Layer / File(s)	Summary
Transaction option derivation and regression coverage packages/client/src/runtime/getPrismaClient.ts, packages/client/tests/functional/interactive-transactions/tests.ts	Nested transactions derive newTxId from the transaction context without mutating input options. Top-level transactions receive undefined. The SQL test verifies that shared options remain unchanged and that a later top-level transaction succeeds.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix · Severity of issue fixed: Medium

Suggested reviewers: voyagerroc-lab

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: preventing nested $transaction from mutating the caller's options object.
Linked Issues check	✅ Passed	Issue #30367 requires $transaction to avoid mutating caller-owned options, derive newTxId from the client transaction scope, prevent polluted options from affecting root transactions, and preserve…
Out of Scope Changes check	✅ Passed	The source change is limited to transaction option construction. The added test directly covers issue #30367 with nested and top-level SQL transactions. No unrelated change is shown in the reviewed di…

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Actionable comments posted: 1

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Inline comments:
In `@packages/client/tests/functional/interactive-transactions/tests.ts`:
- Line 535: Update the assertion on options in the interactive transaction test
to use toStrictEqual instead of toEqual, preserving the expected maxWait and
timeout values while validating the complete object shape and detecting
undefined-valued added keys.

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Reviewing files that changed from the base of the PR and between 8f41a50 and e205a11.

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• packages/client/tests/functional/interactive-transactions/tests.ts

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