fix(session_start): point an installed hook at plumb hooks, not at installing it

CHANGELOG.md

@@ -57,6 +57,15 @@
 
 ### Fixed
 
+- **`session_start` no longer tells you to install a hook you already have.**
+  When a call arrived without a per-call identity, its notice only said
+  "`plumb hooks install claude-code` stamps every call". With the hook
+  installed, the usual cause is a daemon too old to accept the key Claude
+  desktop's connector passes through, so the advice sent people round in a
+  circle. The notice now adds that, if the hook is installed, `plumb hooks`
+  checks it and the daemon: it reports a missing or stale hook, and a daemon
+  that cannot take the stamp.
+
 - **The `git` tool no longer opens an editor.** plumb runs git with no
   terminal, so `rebase --continue`, `rebase -i`, `cherry-pick -e` and
   `revert --edit` launched `core.editor` and failed with `cannot exec

internal/tools/session_start_stamp.go

@@ -66,20 +66,26 @@ func (t *SessionStart) WithStampChannel(fn func(ctx context.Context) StampChanne
 // plumb_agent, the hook works there too, so it is the remedy most callers can
 // apply. The transport remedy (one plumb serve per agent) follows, for a client
 // that cannot stamp at all.
+//
+// For a hook that is already installed it names bare `plumb hooks`, which
+// reports a missing or stale hook and a daemon that cannot take the stamp. It
+// says "checks", not "says why": with a current hook and a daemon that accepts
+// the stamp it has nothing to report, so it cannot promise a diagnosis.
 const stampChannelRefusedNotice = "NOTE: state-changing calls from this session are being refused. " +
 	"This connection serves more than one logical agent and this call carried no per-call identity, " +
 	"so plumb cannot tell which agent's workspace a write belongs to and will not guess. Your session_id " +
 	"declaration IS recorded, but it identifies this call only. Stamp every call: on Claude Code, " +
-	"`plumb hooks install claude-code` (on Claude desktop, restart the app after upgrading plumb); a client " +
-	"whose transport can set it sends a per-call _meta identity; otherwise run one plumb serve per agent.\n"
+	"`plumb hooks install claude-code` (on Claude desktop, restart the app after upgrading plumb); if the hook is " +
+	"installed, `plumb hooks` checks it and the daemon. A client whose transport can set " +
+	"it sends a per-call _meta identity; otherwise run one plumb serve per agent.\n"
 
 // stampChannelDormantNotice is emitted when this call carried no per-call
 // identity but the connection is still single-agent. Nothing is refused yet,
 // so the wording states the future cost rather than a present failure.
 const stampChannelDormantNotice = "NOTE: this call carried no per-call logical-agent identity. Nothing is " +
 	"refused while you are the only agent on this connection, but once a second agent attaches, your " +
 	"unstamped state-changing calls are refused. On Claude Code, `plumb hooks install claude-code` stamps " +
-	"every call.\n"
+	"every call; if the hook is installed, `plumb hooks` checks it and the daemon.\n"
 
 // stampChannelNote renders the disclosure, or "" when there is nothing to say:
 // the accessor is unwired, or the channel is live. Rendered alongside

internal/tools/session_start_stamp_test.go

@@ -165,3 +165,27 @@ func TestStampChannelNoteSilentForNonHookClientUntilShared(t *testing.T) {
 		t.Errorf("a refused non-hook client must be told: %q", got)
 	}
 }
+
+// TestStampChannelNotices_PointAnInstalledHookAtItsDiagnosis: a caller whose
+// hook IS installed but whose call still arrived unstamped (a daemon too old to
+// accept the key Claude desktop's connector passes through) must not be sent to
+// install it again. Both notices name `plumb hooks`, which checks the hook and
+// the daemon it talks to.
+//
+// They must not promise it says WHY: with a current hook and a daemon that
+// accepts its stamp, bare `plumb hooks` has nothing to report (see
+// TestIdentityHookSkewNote in internal/cli), and a promised diagnosis that does
+// not come sends the reader round in a circle again.
+func TestStampChannelNotices_PointAnInstalledHookAtItsDiagnosis(t *testing.T) {
+	for name, notice := range map[string]string{"refused": stampChannelRefusedNotice, "dormant": stampChannelDormantNotice} {
+		if !strings.Contains(notice, "plumb hooks install claude-code") {
+			t.Errorf("%s notice lost the install remedy: %q", name, notice)
+		}
+		if !strings.Contains(notice, "if the hook is installed, `plumb hooks` checks it and the daemon.") {
+			t.Errorf("%s notice does not point an installed hook at `plumb hooks`: %q", name, notice)
+		}
+		if strings.Contains(notice, "says why") {
+			t.Errorf("%s notice promises a diagnosis bare `plumb hooks` does not always give: %q", name, notice)
+		}
+	}
+}