Fix: empty --namespace coerced to __default__ on all vector/record commands

[austin-denoble]

Problem

Fixes #85.

When a user passes --namespace "" to any index vector or record command, the CLI ignores it and silently queries the __default__ namespace instead, returning no results even though vectors exist in the default namespace.

The root cause is in the Go SDK: pc.Index() coerces Namespace: "" to "__default__" unconditionally (go-pinecone client.go:286). This means the literal string "__default__" is sent on the wire over gRPC.

Sending "__default__" requires an active server-side conversion to map it back to "" (the canonical internal representation of the default namespace). That conversion only runs at API version ≥ 2025-04; at older API versions the server actively blocks it with a validation error. By contrast, sending "" directly passes through unchanged on every server version — it is the proto3 zero value for a string field (omitted on the wire) and the server always treats an absent namespace as the default.

Additionally, the Go SDK's assumption was incorrect: "__default__" was introduced as a human-readable alias that clients can send, not the canonical wire format. Clients should send "" and let the server surface "__default__" in responses (which it does at ≥ 2025-04).

Solution

Two changes:

1. sdk.NewIndexConnection: after pc.Index() creates the connection (where the "" → "__default__" coercion happens), immediately re-apply the caller's original namespace via ic.WithNamespace(namespace). WithNamespace sets the field directly, bypassing the coercion. Empty namespace now reaches the gRPC wire as "" (proto3 zero value / omitted field), which the server correctly interprets as the default namespace on all versions.

2. --namespace flag defaults: changed from "__default__" to "" across all eight affected commands (index vector query/upsert/update/fetch/delete/list and index record upsert/search). This makes the CLI default consistent with how the server represents the default namespace (e.g. as shown by pc index stats).

Note: the underlying Go SDK also needs a fix — the coercion at pc.Index() should be removed. The CLI workaround via WithNamespace is sufficient for now but the SDK fix should be tracked separately.

Type of Change

• Bug fix (non-breaking change which fixes an issue)

Test Plan

• just test-unit passes with no failures.
• To validate end-to-end: run pc index stats --index-name <index> on an index with vectors in the default namespace (shows "" key), then confirm pc index vector query --index-name <index> --vector '[...]' --top-k 5 --json returns matches (previously required explicit --namespace __default__ which itself was broken for some users).