feat(hyperguild): brain HTTP REST client

Adds brainClient with Query and Write methods against the brain's
HTTP REST endpoints (/query, /write). Constructor reads BRAIN_URL env
var, defaulting to http://koala:30330 — the Tailscale-exposed
NodePort that serves both MCP and REST.

Tests cover success, transport error, and non-200 cases via
httptest fakes; URL override is verified via t.Setenv.

cmd/hyperguild/http.go

@@ -0,0 +1,117 @@
+package main
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"os"
+	"strconv"
+	"time"
+)
+
+const defaultBrainURL = "http://koala:30330"
+
+// brainClient calls the brain HTTP REST API exposed alongside the MCP
+// endpoint at the same host:port. /mcp serves MCP framing; /query and /write
+// serve plain REST. We use the REST surface because the CLI is a
+// shell-friendly client; MCP framing is unnecessary.
+type brainClient struct {
+	baseURL string
+	http    *http.Client
+}
+
+func newBrainClient() *brainClient {
+	u := os.Getenv("BRAIN_URL")
+	if u == "" {
+		u = defaultBrainURL
+	}
+	return &brainClient{
+		baseURL: u,
+		http:    &http.Client{Timeout: 5 * time.Second},
+	}
+}
+
+// QueryHit mirrors a single result from the brain's /query endpoint.
+type QueryHit struct {
+	Path    string `json:"path"`
+	Title   string `json:"title"`
+	Excerpt string `json:"excerpt"`
+	Score   int    `json:"score"`
+}
+
+// QueryResult mirrors the /query response envelope.
+type QueryResult struct {
+	Results []QueryHit `json:"results"`
+}
+
+func (c *brainClient) Query(ctx context.Context, topic string, limit int) (*QueryResult, error) {
+	q := url.Values{}
+	q.Set("q", topic)
+	q.Set("limit", strconv.Itoa(limit))
+	u := c.baseURL + "/query?" + q.Encode()
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, u, nil)
+	if err != nil {
+		return nil, fmt.Errorf("build request: %w", err)
+	}
+	resp, err := c.http.Do(req)
+	if err != nil {
+		return nil, fmt.Errorf("brain GET /query: %w", err)
+	}
+	defer func() { _ = resp.Body.Close() }()
+	if resp.StatusCode != http.StatusOK {
+		body, _ := io.ReadAll(resp.Body)
+		return nil, fmt.Errorf("brain GET /query: status %d: %s", resp.StatusCode, string(body))
+	}
+	var out QueryResult
+	if err := json.NewDecoder(resp.Body).Decode(&out); err != nil {
+		return nil, fmt.Errorf("decode /query response: %w", err)
+	}
+	return &out, nil
+}
+
+// WriteResult mirrors the /write response envelope.
+type WriteResult struct {
+	Path string `json:"path"`
+}
+
+func (c *brainClient) Write(ctx context.Context, kind, slug string, content io.Reader) (*WriteResult, error) {
+	body, err := io.ReadAll(content)
+	if err != nil {
+		return nil, fmt.Errorf("read content: %w", err)
+	}
+	payload, err := json.Marshal(struct {
+		Type    string `json:"type"`
+		Slug    string `json:"slug"`
+		Content string `json:"content"`
+	}{Type: kind, Slug: slug, Content: string(body)})
+	if err != nil {
+		return nil, fmt.Errorf("marshal payload: %w", err)
+	}
+
+	u := c.baseURL + "/write"
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, u, bytes.NewReader(payload))
+	if err != nil {
+		return nil, fmt.Errorf("build request: %w", err)
+	}
+	req.Header.Set("Content-Type", "application/json")
+
+	resp, err := c.http.Do(req)
+	if err != nil {
+		return nil, fmt.Errorf("brain POST /write: %w", err)
+	}
+	defer func() { _ = resp.Body.Close() }()
+	if resp.StatusCode != http.StatusOK {
+		respBody, _ := io.ReadAll(resp.Body)
+		return nil, fmt.Errorf("brain POST /write: status %d: %s", resp.StatusCode, string(respBody))
+	}
+	var out WriteResult
+	if err := json.NewDecoder(resp.Body).Decode(&out); err != nil {
+		return nil, fmt.Errorf("decode /write response: %w", err)
+	}
+	return &out, nil
+}