[rudycelekli]

Bug

unmarshalLenientJSON (the JSONC fallback added for #922) removes trailing commas with the regex ,\s*([}\]]). The regex has no notion of JSON strings, so it also rewrites , } and , ] inside string values. The fallback runs whenever strict parsing fails, for example on a hand-edited opencode.json with one trailing comma. Connect, disconnect, undo and preview then work on the altered document, and connect writes it back to the client's config file. Another server's arguments are silently changed on disk.

stripJSONComments, the other half of the same fallback, is already string-aware for exactly this reason.

Trigger

~/.config/opencode/opencode.json:

{
  "mcp": {
    "other": {"type": "local", "command": ["sh", "-c", "echo {a, } [b, ]"]},
  },
}

After mcpproxy connect opencode, the other server's command on disk is ["sh", "-c", "echo {a} [b]"].

Fix

Replace the regex with stripTrailingCommas, a small scanner that tracks string and escape state the same way stripJSONComments does. It drops a , only when it is outside a string and the next non-whitespace byte is } or ]. The now-unused regexp import is removed.

Test

TestConnect_TrailingCommaCleanupPreservesStringContents runs a real Connect("opencode", ...) on the file above and checks the other server's command is byte-for-byte unchanged after the write. The existing trailing-comma and JSONC tests still pass.

Commands run

• CGO_ENABLED=0 go vet ./internal/connect: clean
• CGO_ENABLED=0 go test -count=1 ./internal/connect: ok
• With the fix reverted (git stash of connect.go), the new test fails with other server's command rewritten: got ["sh" "-c" "echo {a} [b]"].
• gofmt -l on the edited files: no output

[codecov-commenter]

⚠️ Please install the to ensure uploads and comments are reliably processed by Codecov.

Codecov Report

❌ Patch coverage is 85.18519% with 4 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
internal/connect/connect.go	85.18%	4 Missing ⚠️

📢 Thoughts on this report? Let us know!

[Dumbris]

Verified: the PR test fails on main for the reason described and passes on this branch merged with main; race tests for the touched packages and CI lint (bare and server tags) are clean. Also built and tested together with the rest of this batch, independently reviewed, and cross-reviewed with a second model.

[Dumbris]

Merged. Thank you, @rudycelekli! connect no longer rewrites , } / , ] inside string values of a client's JSONC config.