fix(cli): propagate TLS env vars from .gemini/.env in parent process

[gaurav0107]

Summary

Fixes #25987. NODE_EXTRA_CA_CERTS and other TLS-initialization env
vars defined in .gemini/.env were ignored after PR #24667 introduced
the lightweight parent / heavy child process model, because the
child's Node TLS layer initializes from process.env before its
loadEnvironment() call ever runs.

Details

Node reads NODE_EXTRA_CA_CERTS, SSL_CERT_FILE, HTTPS_PROXY, etc.
once at process start, in C++ before any user JS runs. Pre-#24667 the
CLI ran as a single process, so there was no observable ordering
problem — no outbound TLS happened until after .env was loaded.
After #24667 the child is spawned with a pre-built env, and by the
time the child's JS gets around to parsing .env the TLS layer is
already initialized without the cert.

This PR keeps the parent lightweight (no dotenv import, no heavy
module loads) by hand-parsing .gemini/.env for a small allowlist of
env vars that Node and libcurl require at init time:

• `NODE_EXTRA_CA_CERTS`
• `NODE_TLS_REJECT_UNAUTHORIZED`
• `SSL_CERT_FILE`, `SSL_CERT_DIR`
• `HTTPS_PROXY`, `HTTP_PROXY`, `NO_PROXY`

Values from `.gemini/.env` are injected into the child's spawn env
only when the key is not already set in the shell env, preserving
the existing "shell env wins" rule from `loadEnvironment()`.

Lookup order (matches `findEnvFile` in `settings.ts`):

1. Nearest `/.gemini/.env` walking up parent directories
2. `$HOME/.gemini/.env`

Scope is deliberately narrow: seven well-known network/TLS vars, and
only the `.gemini/.env` path (not arbitrary `.env`). Non-TLS vars
continue to flow through the child's full `loadEnvironment()` path
with its trust checks unchanged.

The PR also adds a small is-main-module guard around `run()` so the
new helpers (`parseSimpleEnv`, `findProjectGeminiEnvFile`,
`loadTlsEnvFromGemini`) can be imported from unit tests without
triggering a child spawn.

Related Issues

Fixes #25987
Related to #24667 (introduced the regression)

How to Validate

1. Create `~/.gemini/.env` with
   `NODE_EXTRA_CA_CERTS=/path/to/cert.pem`.
2. Ensure `NODE_EXTRA_CA_CERTS` is NOT set in your shell env.
3. Run any command that makes an HTTPS request through a CA covered by
   that cert (e.g. `gemini mcp list` against an internal MCP server).
4. Before this PR: `TypeError: fetch failed`.
5. After this PR: succeeds.

Also verified:

• `npm run typecheck --workspace @google/gemini-cli` — clean
• `npx eslint packages/cli/index.ts packages/cli/index.test.ts --max-warnings 0` — clean
• `npx vitest run index.test.ts` — 20/20 new tests pass
• Full `npm run test --workspace @google/gemini-cli` — the 6 unrelated
  failures on my machine (`extension_integrity.json` local-state
  issue) also fail on stock `main`, so they are not regressions
  from this PR.

Pre-Merge Checklist

• Tests added (packages/cli/index.test.ts, 20 cases covering the parser, the dir walker, and the orchestrator helper)
• No breaking changes (helper is additive; existing `newEnv` spread order preserves `process.env` precedence)
• No docs changes needed
• Validated on required platforms/methods:
  • MacOS — npm run, vitest
  • Windows — not available locally (reporter is on win32; reporter steps apply)
  • Linux — not available locally

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a regression where TLS-initialization environment variables defined in .gemini/.env were ignored due to the recent introduction of a parent/child process model. By hand-parsing a specific allowlist of network-critical variables in the lightweight parent process and injecting them into the child's spawn environment, the fix ensures that Node.js correctly picks up these settings before the TLS layer initializes, while preserving existing precedence rules.

Highlights

• TLS Environment Variable Propagation: Implemented a mechanism to parse and propagate critical TLS-related environment variables (e.g., NODE_EXTRA_CA_CERTS) from the user's ~/.gemini/.env file directly into the child process's spawn environment, ensuring they are available during Node.js initialization.
• Lightweight Environment Parser: Added a custom, minimal KEY=VALUE parser to the parent process to avoid loading heavy dependencies like 'dotenv', maintaining the performance benefits of the parent/child process model.
• Testability Improvements: Introduced an 'is-main-module' guard around the CLI's execution logic, allowing helper functions to be imported and unit-tested without triggering the child process spawn.

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[gaurav0107]

Marking this PR ready for review.

Quick summary of what's in the patch:

• Narrowly scoped to $HOME/.gemini/.env in the lightweight parent, so project-local trust logic in the child's loadEnvironment() is not bypassed.
• Seven-key allowlist (NODE_EXTRA_CA_CERTS, NODE_TLS_REJECT_UNAUTHORIZED, SSL_CERT_FILE, SSL_CERT_DIR, HTTPS_PROXY, HTTP_PROXY, NO_PROXY) matches the vars Node and libcurl read before any JS runs.
• Shell-env precedence is preserved (we only inject keys not already in process.env), matching the existing rule in loadEnvironment().
• Hand-rolled parser (~30 LOC) keeps the parent free of dotenv, preserving the startup-latency goal of fix(cli): optimize startup with lightweight parent process #24667.
• 17 unit tests cover quoting, CRLF, export prefix, inline #, malformed lines, allowlist filtering, shell-env precedence, and an explicit assertion that project-local .gemini/.env is not read by the parent.

Happy to iterate on scope, naming, or trust model if reviewers prefer a different cut.

[gemini-code-assist]

Code Review

This pull request introduces a mechanism to propagate TLS and proxy-related environment variables from a user's $HOME/.gemini/.env file to the child process. It includes a lightweight .env parser and a helper function to load allowlisted variables, ensuring that critical settings like NODE_EXTRA_CA_CERTS are available during process initialization. Additionally, the entry point was refactored to support unit testing of these new utilities. I have no feedback to provide.