feat: honour HTTPS_PROXY env var for outbound fetches

[danielroe]

this adds undici as a dep + honors HTTPS_PROXY/HTTP_PROXY environment variables if set and not otherwise configured.

Summary by CodeRabbit

• New Features

  • Support for HTTP/HTTPS proxy via environment variables (HTTPS_PROXY, HTTP_PROXY, and lowercase variants), allowing builds to fetch font data behind corporate proxies without extra setup.

• Documentation

  • README updated to document proxy environment variable support and usage.

[coderabbitai]

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: c0320a2b-d9ce-48be-ba88-471cf648cde8

📥 Commits

Reviewing files that changed from the base of the PR and between 5c6eb4f and dab5893.

📒 Files selected for processing (1)

• test/proxy.test.ts

📝 Walkthrough

Walkthrough

This PR adds HTTP/HTTPS proxy support to unifont by installing undici's EnvHttpProxyAgent as the global fetch dispatcher during startup, enabling font fetches to route through corporate proxies via standard HTTPS_PROXY / HTTP_PROXY environment variables.

Changes

Proxy Support Implementation

Layer / File(s)	Summary
Proxy dispatcher module and dependency src/proxy.ts, package.json	New installProxyDispatcher() function conditionally installs undici's EnvHttpProxyAgent as the process-wide global dispatcher when proxy env vars are present, with idempotency checks and error handling. undici (^7.18.0) added to dependencies.
Integration into createUnifont startup src/unifont.ts	createUnifont imports and awaits installProxyDispatcher() before provider initialization, ensuring proxy configuration is active before font fetches begin.
User-facing documentation README.md	Documentation notes that unifont honors HTTPS_PROXY/HTTP_PROXY environment variables (case-insensitive) for outbound font requests during build time.

🎯 2 (Simple) | ⏱️ ~12 minutes

🐰 A proxy path through corporate walls,
Where unifont's requests now safely crawl,
With undici's agent standing guard,
No more blocked fonts—the PR's not hard!
Environment variables save the day,
Fetch flows through now, hip-hip-hooray! 🎉

🚥 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%.	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 'feat: honour HTTPS_PROXY env var for outbound fetches' accurately describes the main change: adding support for the HTTPS_PROXY environment variable to enable proxy support for outbound font fetches.
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.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix-proxy-support

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.40%. Comparing base (d121188) to head (dab5893).
⚠️ Report is 66 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #404      +/-   ##
==========================================
+ Coverage   98.32%   98.40%   +0.08%     
==========================================
  Files          12       13       +1     
  Lines         656      690      +34     
  Branches      172      180       +8     
==========================================
+ Hits          645      679      +34     
  Misses         11       11              

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@src/proxy.ts`:
- Around line 17-23: The code sets the module-level flag "installed" before
checking for proxy environment variables, preventing future attempts if env vars
are loaded later; move the assignment of installed = true to after detecting a
non-empty proxyUrl (the const proxyUrl = process.env.HTTPS_PROXY ||
process.env.HTTP_PROXY || process.env.https_proxy || process.env.http_proxy) so
that the function returns early without marking installed when no proxy is
configured, and only mark installed once a proxyUrl is found and proxy setup
proceeds.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 57466034-eacf-4f4d-9eed-da5216e76373

📥 Commits

Reviewing files that changed from the base of the PR and between 91f59d2 and 1e56128.

⛔ Files ignored due to path filters (1)

• pnpm-lock.yaml is excluded by !**/pnpm-lock.yaml

📒 Files selected for processing (4)

• README.md
• package.json
• src/proxy.ts
• src/unifont.ts