fix(config): handle $ character with {file:} pattern

[hstove]

What does this PR do?

• Fixes {env:...} variable substitution inconsistently fails for specific MCP server URLs #5299
• Fixes OpenCode crashes on variable substitution if the value contains replacement patterns like $` #11793

This PR fixes an issue where files containing $ would break opencode when your config used the {file:x} pattern. This is because String.prototype.replace treats $ as a replacement character, which is not what we want in this use case. This PR instead uses a replacement function, so that .replace does a "dumb" string replacement.

There is an alternative PR: #11795 . I respectfully believe that that PR's approach is flawed as it tries to escape the $, instead of just treating the $ as-is.

How did you verify your code works?

# verified that this test fails without my fix
cd packages/opencode && bun test test/config/config.test.ts

# verified that this fix works in my project where I hit this bug
bun dev -- ~/my-proj-where-i-found-this-bug

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Duplicate PR Found

PR #11795: #11795

• Title: fix(config): fix variable replacement for files containing dollars
• Reason: This is the alternative PR mentioned in your PR description. Both PRs address the same issues ({env:...} variable substitution inconsistently fails for specific MCP server URLs #5299 and OpenCode crashes on variable substitution if the value contains replacement patterns like $` #11793) regarding handling $ characters in the {file:} pattern. The PR description explicitly notes that PR fix(config): fix variable replacement for files containing dollars #11795 takes a different approach (escaping $) versus your approach (using a replacement function for "dumb" string replacement).

[rekram1-node]

/review

[github-actions]

lgtm