fix(start-client-core): add safe fallback for TSS_SERVER_FN_BASE in createClientRpc

[lx3133584]

Problem

In createClientRpc(), process.env.TSS_SERVER_FN_BASE is evaluated directly to construct the server function URL. In browser environments where globalThis.process is not defined (e.g. Vite dev servers with server.hmr: false where @vite/client preamble is omitted), evaluating process.env throws a ReferenceError: process is not defined. Furthermore, when process.env.TSS_SERVER_FN_BASE is undefined, string concatenation produces "undefined" + functionId, resulting in a relative URL that fails with 500 when called from nested routes.

Root Cause

createClientRpc directly accessed process.env.TSS_SERVER_FN_BASE without guarding against process being undefined or falling back to the default server function base prefix /_serverFn/.

Fix

1. Safely resolve serverFnBase by checking typeof process !== 'undefined' and typeof import.meta !== 'undefined' before reading TSS_SERVER_FN_BASE.
2. Fall back to the standard default /_serverFn/ when TSS_SERVER_FN_BASE is not set.

Testing

1. Added unit tests in packages/start-client-core/tests/createClientRpc.test.ts covering:
   • Custom process.env.TSS_SERVER_FN_BASE resolution
   • Default fallback /_serverFn/ when TSS_SERVER_FN_BASE is undefined
   • Safe execution without ReferenceError when globalThis.process is undefined
2. Ran vitest test suite across start-client-core (91 passed).

Summary by CodeRabbit

• Bug Fixes

  • Improved server-function URL detection across browser and server environments.
  • Prevented errors when the process object is unavailable in browser runtimes.
  • Added support for custom server-function base URLs with a reliable default fallback.

• Tests

  • Added coverage for custom URLs, default behavior, RPC metadata, and environments without process.

[coderabbitai]

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ℹ️ Recent review info

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Run ID: 3e7e4a69-6784-462c-912b-0c43c7f92cb9

📥 Commits

Reviewing files that changed from the base of the PR and between 37877da and 5d1b5e5.

📒 Files selected for processing (2)

• packages/start-client-core/src/client-rpc/createClientRpc.ts
• packages/start-client-core/tests/createClientRpc.test.ts

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📝 Walkthrough

Walkthrough

createClientRpc now resolves its base URL from available environment variables or a default path. Tests cover URL selection, RPC metadata, marker properties, and execution without process.

Changes

Server-function URL resolution

Layer / File(s)	Summary
Environment-safe RPC URL resolution packages/start-client-core/src/client-rpc/createClientRpc.ts, packages/start-client-core/tests/createClientRpc.test.ts	createClientRpc checks guarded process.env and import.meta.env values before using /_serverFn/. Tests validate configured and default URLs, RPC metadata, marker properties, and missing process handling.

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

Merge Risk: ⚪ Minimal · up to 5d1b5

This change prevents browser-side URL construction failures by safely falling back to /_serverFn/ when no server-function base is configured. No actionable merge-blocking risk remains after normal checks and review.

🚥 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
Title check	✅ Passed	The title clearly identifies the primary change: adding safe fallback handling for TSS_SERVER_FN_BASE in createClientRpc.
Description check	✅ Passed	The description clearly explains the problem, root cause, fix, and test coverage. It does not use the template headings or include checklist and release-impact selections, but it remains mostly comple…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

Full details: Description check

Explanation

The description clearly explains the problem, root cause, fix, and test coverage. It does not use the template headings or include checklist and release-impact selections, but it remains mostly complete and directly related to the changes.

• Fix all pre-merge checks with AI

✨ Finishing Touches

🧪 Generate unit tests (beta)

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