diff --git a/workspace-server/internal/handlers/a2a_proxy.go b/workspace-server/internal/handlers/a2a_proxy.go
index 97296d4f..816d5c81 100644
--- a/workspace-server/internal/handlers/a2a_proxy.go
+++ b/workspace-server/internal/handlers/a2a_proxy.go
@@ -21,6 +21,7 @@ import (
 	"time"
 
 	"github.com/Molecule-AI/molecule-monorepo/platform/internal/db"
+	"github.com/Molecule-AI/molecule-monorepo/platform/internal/envx"
 	"github.com/Molecule-AI/molecule-monorepo/platform/internal/events"
 	"github.com/Molecule-AI/molecule-monorepo/platform/internal/models"
 	"github.com/Molecule-AI/molecule-monorepo/platform/internal/provisioner"
@@ -110,11 +111,14 @@ const maxProxyResponseBody = 10 << 20
 //      a generic 502 page to canvas. 10s is well above realistic intra-region
 //      latencies and well below CF's edge timeout.
 //
-//   3. Transport.ResponseHeaderTimeout — 60s. From request-body-end to
-//      response-headers-start. Covers cold-start first-byte (the 30-60s OAuth
-//      flow above), with margin. Body streaming after headers is governed by
-//      the per-request context deadline, NOT this timeout — so multi-minute
-//      agent responses still work fine.
+//   3. Transport.ResponseHeaderTimeout — 180s default. From request-body-end
+//      to response-headers-start. Configurable via
+//      A2A_PROXY_RESPONSE_HEADER_TIMEOUT (envx.Duration). Covers cold-start
+//      first-byte (30-60s OAuth flow above) with enough room for Opus agent
+//      turns (big context + internal delegate_task round-trips routinely exceed
+//      the old 60s ceiling). Body streaming after headers is governed by the
+//      per-request context deadline, NOT this timeout — so multi-minute agent
+//      responses still work fine.
 //
 // The point of (2) and (3) is to surface a *structured* 503 from
 // handleA2ADispatchError when the workspace agent is unreachable, so canvas
@@ -127,7 +131,7 @@ var a2aClient = &http.Client{
 			Timeout:   10 * time.Second,
 			KeepAlive: 30 * time.Second,
 		}).DialContext,
-		ResponseHeaderTimeout: 60 * time.Second,
+		ResponseHeaderTimeout: envx.Duration("A2A_PROXY_RESPONSE_HEADER_TIMEOUT", 180*time.Second),
 		TLSHandshakeTimeout:   10 * time.Second,
 		// MaxIdleConns / IdleConnTimeout: stdlib defaults are fine; agent
 		// fan-in is bounded by the platform's broadcaster fan-out, not by
diff --git a/workspace-server/internal/handlers/a2a_proxy_test.go b/workspace-server/internal/handlers/a2a_proxy_test.go
index ceab1b7c..7fa22dac 100644
--- a/workspace-server/internal/handlers/a2a_proxy_test.go
+++ b/workspace-server/internal/handlers/a2a_proxy_test.go
@@ -2276,3 +2276,43 @@ func TestProxyA2A_PollMode_FailsClosedToPush(t *testing.T) {
 		t.Errorf("unmet sqlmock expectations: %v", err)
 	}
 }
+
+// ==================== a2aClient ResponseHeaderTimeout config ====================
+
+func TestA2AClientResponseHeaderTimeout(t *testing.T) {
+	const defaultTimeout = 180 * time.Second
+
+	// Default (unset env) — a2aClient was initialised at package load time.
+	if a2aClient.Transport.(*http.Transport).ResponseHeaderTimeout != defaultTimeout {
+		t.Errorf("a2aClient default ResponseHeaderTimeout = %v, want %v",
+			a2aClient.Transport.(*http.Transport).ResponseHeaderTimeout, defaultTimeout)
+	}
+
+	// Env var override — verify parsing logic inline since a2aClient is
+	// initialised once at package load (env already consumed at import time).
+	t.Run("A2A_PROXY_RESPONSE_HEADER_TIMEOUT parsed correctly", func(t *testing.T) {
+		// We can't re-initialise a2aClient, but we can verify the same
+		// envx.Duration logic inline for the 5m override case.
+		t.Setenv("A2A_PROXY_RESPONSE_HEADER_TIMEOUT", "5m")
+		if d, err := time.ParseDuration("5m"); err == nil && d > 0 {
+			if d != 5*time.Minute {
+				t.Errorf("ParseDuration(\"5m\") = %v, want 5m", d)
+			}
+		}
+	})
+
+	t.Run("invalid A2A_PROXY_RESPONSE_HEADER_TIMEOUT falls back to default", func(t *testing.T) {
+		t.Setenv("A2A_PROXY_RESPONSE_HEADER_TIMEOUT", "not-a-duration")
+		// Simulate what envx.Duration does with an invalid value.
+		var fallback = 180 * time.Second
+		override := fallback
+		if v := os.Getenv("A2A_PROXY_RESPONSE_HEADER_TIMEOUT"); v != "" {
+			if d, err := time.ParseDuration(v); err == nil && d > 0 {
+				override = d
+			}
+		}
+		if override != fallback {
+			t.Errorf("invalid env var: got %v, want fallback %v", override, fallback)
+		}
+	})
+}