Merge origin/master into v2: sticky-growth test fixed

docs/plans/v2/README.md

@@ -61,3 +61,9 @@ reason.
   procedure. Owner's fault (T19 once more: a new task changed what an earlier given file
   measures, and the pre-handover walk missed it). `helpers_test.go` is now a v2 given file that
   answers `/props` without counting it; resumed.
+- 2026-09-25, task 02: my `TestStickyLeaseSurvivesGrowthUntilItDoesNotFit` "grew" the conversation
+  by enlarging the *first user message*, which by the fingerprint spec makes it a different
+  conversation — so the test demanded `reused` for a new key. Ornith diagnosed it exactly ("turn
+  2's fp differs from turn 1's, yet the test expects reuse") and the session ended on a
+  malformed tool call. Test fault (mine): later turns are now appended after the first user
+  message. Resumed from the working tree.

docs/plans/v2/_files/internal/proxy/ctxguard_test.go

@@ -110,6 +110,13 @@ func TestUnknownContextNeverBlocks(t *testing.T) {
 	}
 }
 
+// grow appends later turns to a conversation body without touching its system prompt or first
+// user message, so the fingerprint — and therefore the lease — stays the same.
+func grow(body string, words int) string {
+	turn := `,{"role":"assistant","content":"ok"},{"role":"user","content":"` + strings.Repeat("x ", words) + `"}`
+	return strings.Replace(body, `]}`, turn+`]}`, 1)
+}
+
 func TestStickyLeaseSurvivesGrowthUntilItDoesNotFit(t *testing.T) {
 	small := ctxUpstream(t, "small", 8192, 2)
 	big := ctxUpstream(t, "big", 131072, 1)
@@ -120,19 +127,18 @@ func TestStickyLeaseSurvivesGrowthUntilItDoesNotFit(t *testing.T) {
 	if resp.Header.Get(proxy.HostHeader) != "small" {
 		t.Fatal("setup: first turn must be on small")
 	}
-	// Same conversation (same first user message), later turn well under 4096: stays.
+	// Same conversation, a later turn well under 4096 tokens: stays.
-	longer := strings.Replace(body, `"content":"`, `"content":"`+strings.Repeat("x ", 500), 1)
+	resp = r.post("/r/v1/chat/completions", grow(body, 500))
-	resp = r.post("/r/v1/chat/completions", longer)
 	drain(resp)
 	if resp.Header.Get(proxy.HostHeader) != "small" || resp.Header.Get(proxy.LeaseHeader) != "reused" {
 		t.Errorf("turn 2: %q %q, want small reused", resp.Header.Get(proxy.HostHeader), resp.Header.Get(proxy.LeaseHeader))
 	}
-	// A turn that outgrows the slot moves the lease — once — and the move is recorded as an event.
+	// A turn that outgrows the slot moves the lease — once — and the move is visible in the header.
-	huge := strings.Replace(body, `"content":"`, `"content":"`+strings.Repeat("x ", 30000), 1)
+	huge := grow(body, 30000)
 	resp = r.post("/r/v1/chat/completions", huge)
 	drain(resp)
-	if resp.StatusCode != 200 || resp.Header.Get(proxy.HostHeader) != "big" {
+	if resp.StatusCode != 200 || resp.Header.Get(proxy.HostHeader) != "big" || !strings.HasPrefix(resp.Header.Get(proxy.CtxHeader), "moved") {
-		t.Fatalf("outgrown turn: %d %q, want 200 from big", resp.StatusCode, resp.Header.Get(proxy.HostHeader))
+		t.Fatalf("outgrown turn: %d %q ctx=%q, want 200 from big with a moved header", resp.StatusCode, resp.Header.Get(proxy.HostHeader), resp.Header.Get(proxy.CtxHeader))
 	}
 	resp = r.post("/r/v1/chat/completions", huge)
 	drain(resp)