diff --git a/CHANGELOG.md b/CHANGELOG.md
index ce7e5216..e128cc66 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -27,6 +27,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 
+- **Plugin releases older than 0.13.0 are marked unsupported**, and lich offers
+  the release it supports in their place. 0.13.0 is the first that tells lich
+  which release it is. Releases older than 0.3.0 can no longer link a session
+  to its conversation, because their old `claude_session_id` field is not read
+  anymore.
+
 - **Installing or updating the lich plugin picks the newest release this lich
   supports, not the newest one published.** In Claude Code and Codex the
   plugin's marketplace is pinned to that release, so those CLIs no longer move
diff --git a/docs/ceilings.md b/docs/ceilings.md
index 2baec3fa..64ebe571 100644
--- a/docs/ceilings.md
+++ b/docs/ceilings.md
@@ -337,9 +337,9 @@ work when nobody knows it and that the call site never shows. The mechanism and
   Neither CLI can change a declared ref, so an install removes the marketplace and adds it back; on Claude Code the
   remove also uninstalls the plugin, and an add that fails there (offline mid-install) leaves it uninstalled until
   the next attempt, which the install prompt then offers. An install that was already outside the range, from
-  before the pin or by hand, is caught by the `X-Lich-Plugin` header its hooks send (docs/hooks/README.md): only
-  once a session reports, and a plugin older than the header sends none, so until the floor passes that release
-  such a plugin is accepted in silence.
+  before the pin or by hand, is caught at startup from its installed version, and again by the `X-Lich-Plugin`
+  header its hooks send (docs/hooks/README.md) once a session reports. A report whose payload lich refuses never
+  reaches that check, so a plugin old enough to send one only shows up in the startup prompt and the log.
 - **The plan gauge answers to two undocumented endpoints, and only two providers have one**
   (`internal/quota`): Claude Code's and Codex's usage routes are what their own CLIs poll, not published API. A
   field renamed upstream drops the window it fed rather than raising anything — an entry lich has no name for is
diff --git a/docs/hooks/README.md b/docs/hooks/README.md
index 8ee35b24..2bb7c83d 100644
--- a/docs/hooks/README.md
+++ b/docs/hooks/README.md
@@ -84,7 +84,8 @@ sent it.
 lich remembers the last release each session named. A release outside the range
 under [Versioning](#versioning) is still applied wherever its payload parses; it
 is logged, and the window offers the release this lich supports. A request with
-no header is a plugin older than the header and is accepted as before.
+no header comes from a plugin older than the header, which is below the floor
+and handled the same way.
 
 ## Client rules (all hooks)
 
diff --git a/docs/hooks/fixtures/README.md b/docs/hooks/fixtures/README.md
index 86564700..b00f5821 100644
--- a/docs/hooks/fixtures/README.md
+++ b/docs/hooks/fixtures/README.md
@@ -41,9 +41,7 @@ Every line carries exactly one of `body` / `raw`, and exactly one of `accept` /
 `accept` is the payload **normalized**, not echoed: it is what the contract's
 defaulting and trimming produce, so it is where `provider` defaults to `claude`
 and a title loses its surrounding whitespace. It lists only the fields a case is
-about — a field absent from `accept` is not asserted, which is how the
-deprecated `claude_session_id` stays out of the expectations while still being
-exercised by the payloads that send it.
+about — a field absent from `accept` is not asserted.
 
 `reject` prose is documentation, not a matcher. lich's error strings are its own
 and change freely; what the fixture fixes is *that* the payload is refused.
diff --git a/docs/hooks/fixtures/session-start.jsonl b/docs/hooks/fixtures/session-start.jsonl
index 2b5d6889..e513a73d 100644
--- a/docs/hooks/fixtures/session-start.jsonl
+++ b/docs/hooks/fixtures/session-start.jsonl
@@ -6,8 +6,6 @@
 {"name":"cursor chat id","body":{"session_id":"s1","provider_session_id":"bec68d79-a208-4e40-8d2f-f8f8964da216","provider":"cursor"},"accept":{"session_id":"s1","provider_session_id":"bec68d79-a208-4e40-8d2f-f8f8964da216","provider":"cursor"}}
 {"name":"kiro session id","body":{"session_id":"s1","provider_session_id":"f5d98acc-da1a-4029-a2eb-ecc1f666af06","provider":"kiro"},"accept":{"session_id":"s1","provider_session_id":"f5d98acc-da1a-4029-a2eb-ecc1f666af06","provider":"kiro"}}
 {"name":"absent provider defaults to claude","body":{"session_id":"s1","provider_session_id":"018f9c5a-0000-7000-9a3b-1c2d3e4f5c01"},"accept":{"session_id":"s1","provider_session_id":"018f9c5a-0000-7000-9a3b-1c2d3e4f5c01","provider":"claude"}}
-{"name":"legacy claude_session_id is folded","body":{"session_id":"s1","claude_session_id":"018f9c5a-0000-7000-9a3b-1c2d3e4f5c02"},"accept":{"session_id":"s1","provider_session_id":"018f9c5a-0000-7000-9a3b-1c2d3e4f5c02","provider":"claude"}}
-{"name":"provider_session_id wins over legacy","body":{"session_id":"s1","provider_session_id":"018f9c5a-0000-7000-9a3b-1c2d3e4f5c01","claude_session_id":"018f9c5a-0000-7000-9a3b-1c2d3e4f5c02"},"accept":{"session_id":"s1","provider_session_id":"018f9c5a-0000-7000-9a3b-1c2d3e4f5c01","provider":"claude"}}
 {"name":"missing session_id","body":{"provider_session_id":"018f9c5a-0000-7000-9a3b-1c2d3e4f5c01"},"reject":"session_id is required"}
 {"name":"missing provider_session_id","body":{"session_id":"s1"},"reject":"provider_session_id is required"}
 {"name":"empty provider_session_id","body":{"session_id":"s1","provider_session_id":""},"reject":"provider_session_id is required"}
diff --git a/docs/hooks/session-start.md b/docs/hooks/session-start.md
index 89e334cc..d467de80 100644
--- a/docs/hooks/session-start.md
+++ b/docs/hooks/session-start.md
@@ -30,9 +30,6 @@ Content-Type: application/json
   field existed. An id outside the registry is rejected, like an unknown state
   on `/hook` — lich ships its side of a contract first, so a provider it has no
   entry for is a client running ahead of it.
-- `claude_session_id` — **deprecated** alias for `provider_session_id`, still
-  accepted so plugin releases before v0.3.0 keep working. When both are
-  present, `provider_session_id` wins. New clients must not send it.
 
 Responses: `204` ok · `401` invalid token · `400` invalid body · `500` lich
 failed to persist.
@@ -85,8 +82,7 @@ scripted run would have said this contract could not be closed.
 
 - **Endpoint** — `internal/terminal/transport.go`, `transport.sessionStart`:
   validates the token and body (`parseSessionStart`) on the same loopback
-  listener as terminal I/O, folds the deprecated `claude_session_id` into
-  `provider_session_id`, defaults an absent `provider` to `claude` and rejects
+  listener as terminal I/O, defaults an absent `provider` to `claude` and rejects
   an unregistered one, then forwards `(session_id, provider_session_id,
   provider)`.
 - **Persistence** — `internal/store/mutations.go`, `Service.SetProviderSession`:
@@ -163,6 +159,3 @@ scripted run would have said this contract could not be closed.
   there and withheld for one that is not. A lock held by the provider running
   right now is waited out briefly and then read as absent — the failure that
   costs a live conversation, which is why the wait exists at all.
-- **The deprecated `claude_session_id` alias stays until the install gate can
-  no longer meet a plugin older than v0.3.0.** Dropping it earlier silently
-  breaks resume for anyone who has not updated the plugin.
diff --git a/internal/agentplugin/agentplugin_test.go b/internal/agentplugin/agentplugin_test.go
index 20f15888..55cf1f43 100644
--- a/internal/agentplugin/agentplugin_test.go
+++ b/internal/agentplugin/agentplugin_test.go
@@ -120,17 +120,17 @@ func TestComputeStatus(t *testing.T) {
 		wantUpdate     bool
 		wantCompatible bool
 	}{
-		{"not installed", false, "", "0.12.2", false, true},
-		{"installed, no latest known", true, "0.12.1", "", false, true},
-		{"update available", true, "0.12.1", "0.12.2", true, true},
-		{"already latest", true, "0.12.2", "0.12.2", false, true},
-		{"installed newer than latest, still compatible", true, "0.13.0", "0.12.2", false, true},
-		{"pre-release install sees the stable release", true, "0.12.0-rc.3", "0.12.0", true, true},
+		{"not installed", false, "", "0.13.2", false, true},
+		{"installed, no latest known", true, "0.13.1", "", false, true},
+		{"update available", true, "0.13.1", "0.13.2", true, true},
+		{"already latest", true, "0.13.2", "0.13.2", false, true},
+		{"installed newer than latest, still compatible", true, "0.13.9", "0.13.2", false, true},
+		{"pre-release install sees the stable release", true, "0.13.1-rc.3", "0.13.1", true, true},
 		// Past the ceiling: the compatible release is offered even though it is
 		// older, because it is the one this lich speaks.
 		{"installed past the ceiling", true, PluginVersionCeiling, "0.13.1", true, false},
-		{"installed below the floor", true, "0.2.9", "0.13.1", true, false},
-		{"incompatible, no compatible release known", true, "0.2.9", "", false, false},
+		{"installed below the floor", true, "0.12.9", "0.13.1", true, false},
+		{"incompatible, no compatible release known", true, "0.12.9", "", false, false},
 	}
 	for _, tc := range tests {
 		t.Run(tc.name, func(t *testing.T) {
@@ -279,9 +279,9 @@ func statusOf(t *testing.T, list []Status, provider string) Status {
 }
 
 func TestStatus(t *testing.T) {
-	t.Setenv("CLAUDE_CONFIG_DIR", writeClaudeState(t, `{"plugins":{"lich@lich-plugin":[{"scope":"user","version":"0.12.0-rc.3"}]}}`))
+	t.Setenv("CLAUDE_CONFIG_DIR", writeClaudeState(t, `{"plugins":{"lich@lich-plugin":[{"scope":"user","version":"0.13.1-rc.3"}]}}`))
 
-	s := serveBody(t, http.StatusOK, `[{"tag_name":"v0.12.0"}]`)
+	s := serveBody(t, http.StatusOK, `[{"tag_name":"v0.13.1"}]`)
 	// Codex's version comes from its CLI, which is not spawned here; only the
 	// Claude Code entry is asserted on.
 	s.lookPath = func(name string) (string, error) {
@@ -293,7 +293,7 @@ func TestStatus(t *testing.T) {
 
 	want := Status{
 		Provider: providers.Claude, Name: "Claude Code", Available: true,
-		Installed: true, InstalledVersion: "0.12.0-rc.3", LatestVersion: "0.12.0", UpdateAvailable: true,
+		Installed: true, InstalledVersion: "0.13.1-rc.3", LatestVersion: "0.13.1", UpdateAvailable: true,
 		Compatible: true,
 	}
 	if got := statusOf(t, s.Status(), providers.Claude); got != want {
@@ -306,7 +306,7 @@ func TestStatus(t *testing.T) {
 // install button on a CLI with nothing to install.
 func TestStatusListsEveryHarness(t *testing.T) {
 	t.Setenv("CLAUDE_CONFIG_DIR", t.TempDir())
-	s := serveBody(t, http.StatusOK, `[{"tag_name":"v0.12.0"}]`)
+	s := serveBody(t, http.StatusOK, `[{"tag_name":"v0.13.1"}]`)
 	s.lookPath = func(string) (string, error) { return "", errors.New("not found") }
 
 	var got []string
@@ -339,14 +339,14 @@ func TestStatusWithoutTheCLI(t *testing.T) {
 
 func TestStatusNotInstalled(t *testing.T) {
 	t.Setenv("CLAUDE_CONFIG_DIR", t.TempDir())
-	s := serveBody(t, http.StatusOK, `[{"tag_name":"v0.12.0"}]`)
+	s := serveBody(t, http.StatusOK, `[{"tag_name":"v0.13.1"}]`)
 
 	got := statusOf(t, s.Status(), providers.Claude)
 	if got.Installed || got.UpdateAvailable {
 		t.Fatalf("Status() = %+v, want not installed and no update", got)
 	}
-	if got.LatestVersion != "0.12.0" {
-		t.Fatalf("LatestVersion = %q, want %q", got.LatestVersion, "0.12.0")
+	if got.LatestVersion != "0.13.1" {
+		t.Fatalf("LatestVersion = %q, want %q", got.LatestVersion, "0.13.1")
 	}
 }
 
diff --git a/internal/agentplugin/compat.go b/internal/agentplugin/compat.go
index a7e421cf..52a229e6 100644
--- a/internal/agentplugin/compat.go
+++ b/internal/agentplugin/compat.go
@@ -9,9 +9,10 @@ import (
 // change (its major, from 1.0) and its patch for anything else, so every release
 // below the ceiling sends only what this lich accepts.
 const (
-	// PluginVersionFloor is the oldest plugin release whose reports this lich
-	// still parses.
-	PluginVersionFloor = "0.3.0"
+	// PluginVersionFloor is the oldest plugin release this lich supports: the
+	// first to name itself in the X-Lich-Plugin header, so every supported
+	// install says which release a report comes from.
+	PluginVersionFloor = "0.13.0"
 	// PluginVersionCeiling is the first release past the newest contract this
 	// lich implements (0.13), and the first one it cannot vouch for.
 	PluginVersionCeiling = "0.14.0"
diff --git a/internal/agentplugin/compat_test.go b/internal/agentplugin/compat_test.go
index 5281323a..c6875b5c 100644
--- a/internal/agentplugin/compat_test.go
+++ b/internal/agentplugin/compat_test.go
@@ -6,8 +6,9 @@ import "testing"
 // moving a bound is a visible edit here too.
 func TestCompatible(t *testing.T) {
 	tests := map[string]bool{
-		"0.2.9":        false,
-		"0.3.0":        true,
+		"0.12.9":       false,
+		"0.13.0-rc.1":  false,
+		"0.13.0":       true,
 		"0.13.9":       true,
 		"0.14.0-rc.1":  true,
 		"0.14.0":       false,
@@ -28,9 +29,9 @@ func TestNewestCompatible(t *testing.T) {
 		tags []string
 		want string
 	}{
-		{"newest in range wins over a newer one past it", []string{"0.14.0", "0.13.2", "0.13.10", "0.12.0"}, "0.13.10"},
-		{"order does not matter", []string{"0.12.0", "0.13.1"}, "0.13.1"},
-		{"nothing in range", []string{"0.14.0", "0.2.0"}, ""},
+		{"newest in range wins over a newer one past it", []string{"0.14.0", "0.13.2", "0.13.10", "0.12.9"}, "0.13.10"},
+		{"order does not matter", []string{"0.13.0", "0.13.1"}, "0.13.1"},
+		{"nothing in range", []string{"0.14.0", "0.12.0"}, ""},
 		{"no releases", nil, ""},
 	}
 	for _, tc := range tests {
diff --git a/internal/agentplugin/files_test.go b/internal/agentplugin/files_test.go
index 8891ebc8..6f78dc30 100644
--- a/internal/agentplugin/files_test.go
+++ b/internal/agentplugin/files_test.go
@@ -23,7 +23,7 @@ import (
 // release published, the marker that names the version, and — for Crush — that
 // every line the user wrote survives the write.
 
-const testVersion = "0.8.0"
+const testVersion = "0.13.0"
 
 // fileServer serves the plugin repository's files at a tag and records the
 // paths asked for. A path with no body 404s, which is how a test says "this
diff --git a/internal/terminal/pluginversion.go b/internal/terminal/pluginversion.go
index 4300e47c..55dbdff1 100644
--- a/internal/terminal/pluginversion.go
+++ b/internal/terminal/pluginversion.go
@@ -45,8 +45,7 @@ type pluginVersions struct {
 }
 
 // note records the release a session's report named. An absent header is a
-// plugin older than the header itself, whose reports are accepted as they
-// always were; it is recorded but raises nothing.
+// plugin older than the header, and so older than the floor.
 func (p *pluginVersions) note(id, version string) {
 	p.mu.Lock()
 	if p.byID == nil {
@@ -57,10 +56,10 @@ func (p *pluginVersions) note(id, version string) {
 	fn := p.onIncompatible
 	p.mu.Unlock()
 
-	if (seen && prev == version) || version == "" || agentplugin.Compatible(version) {
+	if (seen && prev == version) || agentplugin.Compatible(version) {
 		return
 	}
-	slog.Warn("hook: plugin outside the supported range", "session", id, "plugin", version,
+	slog.Warn("hook: plugin outside the supported range", "session", id, "plugin", pluginLabel(version),
 		"floor", agentplugin.PluginVersionFloor, "ceiling", agentplugin.PluginVersionCeiling)
 	if fn != nil {
 		fn(id, version)
diff --git a/internal/terminal/pluginversion_test.go b/internal/terminal/pluginversion_test.go
index 485897e2..2661cabe 100644
--- a/internal/terminal/pluginversion_test.go
+++ b/internal/terminal/pluginversion_test.go
@@ -30,7 +30,7 @@ func TestPluginVersionsRaisesOncePerSessionAndRelease(t *testing.T) {
 	raised := incompatibleRecorder(&p)
 
 	p.note("a", "0.13.0") // compatible
-	p.note("a", "")       // a plugin older than the header
+	p.note("a", "")       // a plugin older than the header, so below the floor
 	p.note("a", "9.0.0")
 	p.note("a", "9.0.0") // repeat report, same release
 	p.note("b", "9.0.0") // another session
@@ -39,7 +39,7 @@ func TestPluginVersionsRaisesOncePerSessionAndRelease(t *testing.T) {
 	p.forget("b")
 	p.note("b", "9.0.0") // a closed session's id reused
 
-	want := []string{"a@9.0.0", "b@9.0.0", "a@9.0.0", "b@9.0.0"}
+	want := []string{"a@", "a@9.0.0", "b@9.0.0", "a@9.0.0", "b@9.0.0"}
 	if got := raised(); !slices.Equal(got, want) {
 		t.Fatalf("raised %v, want %v", got, want)
 	}
diff --git a/internal/terminal/transport.go b/internal/terminal/transport.go
index 4713cf9a..bba62fd5 100644
--- a/internal/terminal/transport.go
+++ b/internal/terminal/transport.go
@@ -505,15 +505,11 @@ func clampRunes(s string, max int) string {
 	return string(runes[:max])
 }
 
-// startRequest is a session-start POST body. LegacyClaudeSessionID accepts the
-// pre-multi-provider field name plugin releases before v0.3.0 send; parsing
-// folds it into ProviderSessionID, so nothing downstream sees two names. Drop it
-// once the install gate can no longer meet an older plugin.
+// startRequest is a session-start POST body.
 type startRequest struct {
-	SessionID             string `json:"session_id"`
-	ProviderSessionID     string `json:"provider_session_id"`
-	Provider              string `json:"provider"`
-	LegacyClaudeSessionID string `json:"claude_session_id"`
+	SessionID         string `json:"session_id"`
+	ProviderSessionID string `json:"provider_session_id"`
+	Provider          string `json:"provider"`
 }
 
 // sessionStart receives the session-start POST from a provider's hook running
@@ -541,9 +537,6 @@ func parseSessionStart(body []byte) (startRequest, error) {
 	if err := json.Unmarshal(body, &req); err != nil {
 		return startRequest{}, fmt.Errorf("invalid session-start body: %w", err)
 	}
-	if req.ProviderSessionID == "" {
-		req.ProviderSessionID = req.LegacyClaudeSessionID
-	}
 	if req.Provider == "" {
 		req.Provider = providers.Claude
 	}
diff --git a/internal/terminal/transport_test.go b/internal/terminal/transport_test.go
index 6eef004e..08745a89 100644
--- a/internal/terminal/transport_test.go
+++ b/internal/terminal/transport_test.go
@@ -407,10 +407,8 @@ func TestParseSessionStart(t *testing.T) {
 		wantErr        bool
 	}{
 		{"ok", `{"session_id":"s1","provider_session_id":"uuid-1"}`, "s1", "uuid-1", "claude", false},
-		{"legacy claude field", `{"session_id":"s1","claude_session_id":"uuid-2"}`, "s1", "uuid-2", "claude", false},
-		{"new field wins over legacy",
-			`{"session_id":"s1","provider_session_id":"uuid-1","claude_session_id":"uuid-2"}`,
-			"s1", "uuid-1", "claude", false},
+		// The pre-0.3.0 alias is gone: the floor is past every plugin that sent it.
+		{"legacy claude field is not read", `{"session_id":"s1","claude_session_id":"uuid-2"}`, "", "", "", true},
 		{"reported provider",
 			`{"session_id":"s1","provider_session_id":"uuid-1","provider":"codex"}`,
 			"s1", "uuid-1", "codex", false},
@@ -439,9 +437,6 @@ func TestParseSessionStart(t *testing.T) {
 		{"question mark provider id",
 			`{"session_id":"s1","provider_session_id":"uuid-?"}`,
 			"", "", "", true},
-		{"legacy field is checked too",
-			`{"session_id":"s1","claude_session_id":"../../etc/passwd"}`,
-			"", "", "", true},
 		{"a dot inside an id is not a traversal",
 			`{"session_id":"s1","provider_session_id":"ses.2026-08-17.a1b2"}`,
 			"s1", "ses.2026-08-17.a1b2", "claude", false},