fix(postgres): use net.JoinHostPort to support IPv6 hosts

[kaldown]

Summary

The postgres source built its connection URL with fmt.Sprintf("%s:%s", host, port), which produces invalid authority for IPv6 literals. pgx then parsed the result as an 8-segment IPv6 with the port absorbed as a trailing hextet, producing dial errors such as:

dial tcp [fd00::1:5432]:5432: connect: no route to host

Replacing the concatenation with net.JoinHostPort wraps IPv6 literals in brackets as required by RFC 3986, and leaves IPv4 addresses and hostnames unchanged.

URL construction is extracted into a new BuildPostgresURL helper so it can be unit-tested without a live database.

Changes

• internal/sources/postgres/postgres.go
  • Introduce BuildPostgresURL that uses net.JoinHostPort.
  • Encode query parameters with url.Values.Encode() (per gemini-code-assist review): proper escaping of &, =, spaces, and deterministic key order.
  • Remove the now-unused ConvertParamMapToRawQuery helper. It was only referenced from this file; internal/sources/cockroachdb has its own independent copy and is not affected.
• internal/sources/postgres/postgres_test.go
  • Add TestBuildPostgresURL covering hostname, IPv4 (127.0.0.1), IPv6 loopback (::1), IPv6 documentation (2001:db8::1), query-parameter key ordering, and URL-encoding of values containing special characters. Each expected URL is also fed through pgx.ParseConfig to verify downstream compatibility.
  • Drop TestConvertParamMapToRawQuery alongside the removed function.

Backward compatibility

• net.JoinHostPort behaves identically to fmt.Sprintf("%s:%s", host, port) for hostnames and IPv4 addresses — brackets are only added when the host contains a colon.
• The query-string output order is now deterministic (sorted by key) rather than map-iteration order. The previous order was already non-deterministic, so any consumer that depended on a specific order was already broken.
• queryParams values that previously contained special characters such as & or = would have produced malformed URLs; they are now correctly percent-encoded.

Test plan

• go test ./internal/sources/postgres/... — all tests pass including new IPv6 and query-param encoding cases.
• go vet ./internal/sources/postgres/... — clean.
• End-to-end: built the patched toolbox and used it via --prebuilt postgres --stdio to connect to a real PostgreSQL instance reachable only over IPv6 (ULA address via a WireGuard-style tunnel). The MCP client listed tools and executed queries successfully, whereas the unpatched binary failed with the mangled dial error shown above.

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[gemini-code-assist]

Code Review

This pull request introduces a BuildPostgresURL helper function in the Postgres source to correctly handle IPv6 addresses using net.JoinHostPort and adds corresponding unit tests. Feedback was provided to improve the robustness of URL generation by using url.Values for query parameter encoding instead of the manual concatenation method, ensuring special characters are correctly escaped and parameters are ordered deterministically.

[kaldown]

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