diff --git a/zig/src/server/root.zig b/zig/src/server/root.zig
index c7b31b5004..6322e35725 100644
--- a/zig/src/server/root.zig
+++ b/zig/src/server/root.zig
@@ -80,6 +80,8 @@ test {
     _ = @import("slide_recheck.zig");
     _ = @import("slide_forget.zig");
     _ = @import("slide_forget_test.zig");
+    _ = @import("slide_teacher_test.zig");
+    _ = @import("slide_learn_path_test.zig");
     _ = @import("slide_whom.zig");
     _ = @import("slide_subject.zig");
     _ = @import("slide_span.zig");
diff --git a/zig/src/server/slide.zig b/zig/src/server/slide.zig
index 147945544c..6b3623a20f 100644
--- a/zig/src/server/slide.zig
+++ b/zig/src/server/slide.zig
@@ -126,6 +126,7 @@ pub fn learn(srv: *Server, conn: *Conn, a: Allocator) void {
         srv.slide.expects(id, expected(a, plan));
         const result = rounds(srv, a, &cx, plan, gone, id);
         const back = result.recalled.len == 1 and result.recalled[0];
+        srv.teacher.ended(back); // a lesson given up leaves the next one's checks as if it never ran
         if (!back) putBack(srv, a, gave, id);
         if (back) slide_teacher.refresh(srv, &cx, &srv.teacher, plan.stale, gone) catch srv.teacher.forgetAnswers(srv.io);
         if (result.why) |why| srv.slide.note(id, why);
diff --git a/zig/src/server/slide_learn_path_test.zig b/zig/src/server/slide_learn_path_test.zig
new file mode 100644
index 0000000000..e3b665e75f
--- /dev/null
+++ b/zig/src/server/slide_learn_path_test.zig
@@ -0,0 +1,250 @@
+//! slide.learn end to end over a scripted model: a lesson given up between two kept ones leaves the later one's checks.
+const std = @import("std");
+const platform = @import("sys");
+const api = @import("engine_api");
+const json = @import("json");
+const model_text = @import("model_text.zig");
+const routes = @import("routes.zig");
+const prompts = @import("slide_prompts.zig");
+const Server = @import("server.zig").Server;
+const Conn = @import("http_conn.zig").Conn;
+const Allocator = std.mem.Allocator;
+const testing = std.testing;
+
+/// Renders every message as ROLE:CONTENT| and the reply's head as A:, bytes as tokens.
+const Text = struct {
+    fn text(t: *@This()) model_text.Text {
+        return .{ .ctx = t, .vtable = &.{ .encode = encode, .decode = decode, .token_id = tokenId, .token_string = tokenString, .vocab_size = vocabSize, .eos_ids = eosIds, .render = render, .template_source = templateSource } };
+    }
+    fn encode(_: *anyopaque, a: Allocator, input: []const u8, _: bool) model_text.Error![]u32 {
+        const ids = try a.alloc(u32, input.len);
+        for (input, ids) |b, *id| id.* = b;
+        return ids;
+    }
+    fn decode(_: *anyopaque, a: Allocator, ids: []const u32) Allocator.Error![]u8 {
+        var out: std.ArrayList(u8) = .empty;
+        for (ids) |id| if (id < 256) try out.append(a, @intCast(id));
+        return out.toOwnedSlice(a);
+    }
+    fn tokenId(_: *anyopaque, _: []const u8) ?u32 {
+        return null;
+    }
+    fn tokenString(_: *anyopaque, a: Allocator, id: u32) Allocator.Error![]u8 {
+        return std.fmt.allocPrint(a, "{d}", .{id});
+    }
+    fn vocabSize(_: *anyopaque) u32 {
+        return 256;
+    }
+    fn eosIds(_: *anyopaque) []const u32 {
+        return &.{};
+    }
+    fn render(_: *anyopaque, a: Allocator, messages: json.Value, o: model_text.RenderOptions, _: *[]const u8) model_text.Error![]u8 {
+        var out: std.ArrayList(u8) = .empty;
+        for (messages.items() orelse &.{}) |m| try out.print(a, "{s}:{s}|", .{ m.strField("role") orelse "", m.strField("content") orelse "" });
+        if (o.add_generation_prompt) try out.appendSlice(a, "A:") else try out.appendSlice(a, "E|");
+        return out.toOwnedSlice(a);
+    }
+    fn templateSource(_: *anyopaque) []const u8 {
+        return "";
+    }
+};
+
+/// A fact the scripted model knows how to be asked about: its words, the kind of thing, and the questions it gets.
+const Topic = struct { fact: []const u8, value: []const u8, kind: []const u8 };
+
+const topics = [_]Topic{
+    .{ .fact = "I like blue.", .value = "blue", .kind = "colour" },
+    .{ .fact = "I like apples.", .value = "apples", .kind = "fruit" },
+    .{ .fact = "I like tea.", .value = "tea", .kind = "drink" },
+};
+
+fn has(text: []const u8, word: []const u8) bool {
+    return std.ascii.findIgnoreCase(text, word) != null;
+}
+
+/// The scripted model: answers the lesson writer's prompts, and the taught model answers the facts it holds.
+const Model = struct {
+    gives_up: []const u8 = "", // a fact whose lessons never bring it back
+    live: [topics.len]bool = @splat(false), // the facts the pocket holds now
+    open: ?usize = null, // the fact the lesson running now teaches
+    trained: std.ArrayList([]const u8) = .empty, // per kept lesson: the personal prompts it trained to keep, joined
+    pending: std.ArrayList(u8) = .empty, // the open lesson's personal keep prompts
+    lessons: u32 = 0,
+    gpa: Allocator = testing.allocator,
+
+    fn engine(m: *Model) api.Engine {
+        return .{ .ctx = m, .vtable = &.{ .info = info, .submit = submit, .cancel = cancel, .status = status, .memory = memory, .learn = learn } };
+    }
+    fn deinit(m: *Model) void {
+        for (m.trained.items) |t| m.gpa.free(t);
+        m.trained.deinit(m.gpa);
+        m.pending.deinit(m.gpa);
+    }
+    fn info(_: *anyopaque) api.Info {
+        return .{};
+    }
+    fn topicOf(text: []const u8) ?usize {
+        // the fact's own words first, the first named (a writer's prompt quotes the fact before its examples)
+        inline for (.{ "fact", "value", "kind" }) |field| {
+            var best: ?usize = null;
+            var at: usize = std.math.maxInt(usize);
+            for (topics, 0..) |t, i| if (std.ascii.findIgnoreCase(text, @field(t, field))) |x| if (x < at) {
+                at = x;
+                best = i;
+            };
+            if (best) |b| return b;
+        }
+        return null;
+    }
+    fn questions(a: Allocator, t: Topic, n: usize) ![]const u8 {
+        const forms = [_][]const u8{ "What {s} do I like?", "Which {s} do I like?", "What is my favourite {s}?", "Tell me the {s} I like.", "Which {s} is my favourite?", "What {s} did I say I like?", "Do you know what {s} I like?", "What {s} do I enjoy?", "Name the {s} I like.", "Which {s} do I love?", "What kind of {s} do I like?", "What {s} am I fond of?" };
+        var out: std.ArrayList(u8) = .empty;
+        for (0..@min(n, forms.len)) |i| {
+            try out.print(a, "{d}. ", .{i + 1});
+            const f = forms[i];
+            const at = std.mem.indexOf(u8, f, "{s}").?;
+            try out.print(a, "{s}{s}{s}\n", .{ f[0..at], t.kind, f[at + 3 ..] });
+        }
+        return out.items;
+    }
+    fn reply(m: *Model, a: Allocator, prompt: []const u8, untaught: bool) ![]const u8 {
+        const user_at = std.mem.lastIndexOf(u8, prompt, "user:") orelse 0;
+        const user = prompt[user_at..];
+        const system = prompt[0..user_at];
+        if (has(user, "Write ") and has(user, "questions")) {
+            const t = topicOf(user) orelse return "1. What is my name?\n";
+            if (has(user, "yes-or-no")) return "1. Do I like red?\n2. Do I like green?\n3. Do I like grey?\n4. Do I like pink?\n";
+            if (has(user, "does not answer") or has(user, "something else")) return "1. What colour is my car?\n2. Where do I live?\n3. What is my job?\n4. What is my dog's name?\n5. What sport do I play?\n6. What is my age?\n";
+            return questions(a, topics[t], 12);
+        }
+        if (has(user, "Rewrite each to start with")) return "1. Do you remember what colour I like?\n2. Do you know what fruit I like?\n";
+        if (has(user, "write two questions worded almost the same")) return "1. What colour does my sister like?\n2. What colour does my brother like?\n";
+        if (has(user, "List six other things")) return "car\nhouse\nshirt\nhat\nbike\nphone\n";
+        if (has(user, "Reply with its number only")) return "0";
+        if (has(user, "What language")) return "English";
+        if (has(user, "Reply yes or no") or has(user, "(answer yes)") or has(user, "Does B tell")) {
+            if (has(user, "Does it answer this question")) return if (topicOf(user)) |_| "yes" else "no";
+            return "no";
+        }
+        if (has(user, "Who or what is this fact about")) return "I";
+        if (has(user, "What is this question asking about")) return "what I like";
+        if (has(user, "Using only that, answer")) return if (topicOf(user)) |t| topics[t].value else "not stated";
+        // a question asked with the fact before it (the lesson's own answers), or of the taught model
+        const t = topicOf(user) orelse return if (has(user, "Hello")) "Hello." else "I don't know.";
+        if (has(system, "told you") or has(system, "You know this")) return if (has(user, "few words")) topics[t].value else try std.fmt.allocPrint(a, "You like {s}.", .{topics[t].value});
+        if (!untaught and m.live[t]) return try std.fmt.allocPrint(a, "You like {s}.", .{topics[t].value});
+        return "I don't know.";
+    }
+    fn submit(ctx: *anyopaque, id: api.Id, request: *const api.Request, sink: api.Sink) api.SubmitError!void {
+        const m: *Model = @ptrCast(@alignCast(ctx));
+        var arena: std.heap.ArenaAllocator = .init(m.gpa);
+        defer arena.deinit();
+        const a = arena.allocator();
+        const prompt = a.alloc(u8, request.prompt.len) catch return error.Busy;
+        for (request.prompt, prompt) |x, *b| b.* = @intCast(x);
+        const said = m.reply(a, prompt, request.untaught) catch return error.Busy;
+        const ids = a.alloc(u32, said.len) catch return error.Busy;
+        for (said, ids) |b, *x| x.* = b;
+        sink.event(sink.ctx, id, &.{ .prefilled = 0 });
+        sink.event(sink.ctx, id, &.{ .tokens = ids });
+        sink.event(sink.ctx, id, &.{ .finished = .{ .reason = .stop } });
+    }
+    fn cancel(_: *anyopaque, _: api.Id) void {}
+    fn status(_: *anyopaque, out: *api.Status, _: []u32) void {
+        out.* = .{};
+    }
+    fn memory(_: *anyopaque, _: bool) ?api.Memory {
+        return null;
+    }
+    fn learn(ctx: *anyopaque, request: *const api.LearnRequest, sink: api.LearnSink) api.LearnError!void {
+        const m: *Model = @ptrCast(@alignCast(ctx));
+        if (request.drop or request.undo) {
+            if (m.open) |t| m.live[t] = false;
+            m.pending.clearRetainingCapacity();
+            m.open = null;
+            return sink.event(sink.ctx, &.{ .done = .{} });
+        }
+        if (request.train.len > 0 and !request.more) {
+            // a new lesson: which fact it teaches, and the personal prompts it keeps as they are
+            var buf: [512]u8 = undefined;
+            const ex = request.train[0];
+            const n = @min(buf.len, ex.ids.len);
+            for (ex.ids[0..n], buf[0..n]) |x, *b| b.* = @intCast(x);
+            m.open = topicOf(buf[0..n]);
+            m.pending.clearRetainingCapacity();
+            for (request.keep) |k| {
+                var kb: [512]u8 = undefined;
+                const kn = @min(kb.len, k.ids.len);
+                for (k.ids[0..kn], kb[0..kn]) |x, *b| b.* = @intCast(x);
+                for (prompts.personal_prompts, 0..) |p, i| if (std.mem.indexOf(u8, kb[0..kn], p) != null) m.pending.print(m.gpa, "{d},", .{i}) catch {};
+            }
+        }
+        const t = m.open orelse return sink.event(sink.ctx, &.{ .done = .{} });
+        const back = !std.mem.eql(u8, topics[t].fact, m.gives_up);
+        if (request.train.len > 0) {
+            m.live[t] = back;
+            sink.event(sink.ctx, &.{ .learned = .{ .recalled = back, .steps = 1, .loss = 0 } });
+        }
+        if (request.save and back and m.pending.items.len > 0) {
+            m.trained.append(m.gpa, m.gpa.dupe(u8, m.pending.items) catch "") catch {};
+            m.pending.clearRetainingCapacity();
+        }
+        sink.event(sink.ctx, &.{ .done = .{} });
+    }
+};
+
+/// One POST /v1/slide/learn through the router, its whole event stream read.
+fn learnOne(srv: *Server, text: []const u8) !void {
+    var pair: [2]platform.posix.socket_t = undefined;
+    if (platform.windows) {
+        try platform.posix.socketpair(&pair);
+    } else if (platform.c.socketpair(std.posix.AF.UNIX, std.posix.SOCK.STREAM, 0, &pair) != 0) return error.SocketPair;
+    defer _ = platform.posix.system.close(pair[0]);
+    defer _ = platform.posix.system.close(pair[1]);
+    var arena: std.heap.ArenaAllocator = .init(testing.allocator);
+    defer arena.deinit();
+    const a = arena.allocator();
+    const body = try std.fmt.allocPrint(a, "{{\"text\": \"{s}\"}}", .{text});
+    const head = try std.fmt.allocPrint(a, "POST /v1/slide/learn HTTP/1.1\r\nHost: t\r\nContent-Length: {d}\r\n\r\n{s}", .{ body.len, body });
+    _ = platform.posix.system.write(pair[0], head.ptr, head.len);
+    var conn = try Conn.init(testing.allocator, pair[1], "test");
+    defer conn.deinit();
+    conn.timeouts = .{ .idle_ms = 5000, .read_ms = 5000, .write_ms = 5000 };
+    if (try conn.readRequest(a, false) != .ready) return error.BadRequest;
+    const Drain = struct {
+        fn run(fd: platform.posix.socket_t) void {
+            var buf: [4096]u8 = undefined;
+            while (platform.posix.system.read(fd, &buf, buf.len) > 0) {}
+        }
+    };
+    const drain = try std.Thread.spawn(.{}, Drain.run, .{pair[0]});
+    routes.dispatch(srv, &conn, a);
+    _ = platform.posix.system.shutdown(pair[1], platform.posix.SHUT.WR);
+    _ = platform.posix.system.shutdown(pair[0], platform.posix.SHUT.WR);
+    drain.join();
+}
+
+/// The personal prompts each kept lesson trained to keep, after teaching `facts` in turn (one gives up when told).
+fn teach(gives_up: []const u8, facts: []const []const u8) !Model {
+    var text: Text = .{};
+    var m: Model = .{ .gives_up = gives_up };
+    const srv = try Server.init(testing.allocator, testing.io, m.engine(), text.text(), .{ .served_name = "m", .model_ids = &.{"m"}, .enable_thinking = false, .use_drafts = false }, null);
+    defer srv.deinit();
+    for (facts) |f| try learnOne(srv, f);
+    return m;
+}
+
+test "through slide.learn, a lesson given up between two kept ones leaves the second kept lesson's checks" {
+    // the given-up lesson ("I like apples.") between the two kept ones, and the same two kept lessons alone
+    var with = try teach("I like apples.", &.{ "I like blue.", "I like apples.", "I like tea." });
+    defer with.deinit();
+    var without = try teach("", &.{ "I like blue.", "I like tea." });
+    defer without.deinit();
+    try testing.expectEqual(@as(usize, 2), without.trained.items.len);
+    try testing.expectEqual(@as(usize, 2), with.trained.items.len); // the given-up lesson kept nothing
+    try testing.expectEqualStrings(without.trained.items[0], with.trained.items[0]);
+    // the kept lesson after the given-up one trains on the personal prompts it would have had without it
+    try testing.expectEqualStrings(without.trained.items[1], with.trained.items[1]);
+    // control: the held-back prompts do turn from one kept lesson to the next
+    try testing.expect(!std.mem.eql(u8, without.trained.items[0], without.trained.items[1]));
+}
diff --git a/zig/src/server/slide_lesson.zig b/zig/src/server/slide_lesson.zig
index 6ab8e20909..6a03b72b3e 100644
--- a/zig/src/server/slide_lesson.zig
+++ b/zig/src/server/slide_lesson.zig
@@ -116,11 +116,11 @@ pub fn lesson(srv: *Server, cx: *Cx, teacher: *Teacher, told: []const []const u8
     // what the change must never touch: questions about the user and prompts of every kind, as the model answers them
     var keep: std.ArrayList(api.Example) = .empty;
     var checks: std.ArrayList(Check) = .empty;
-    teacher.lessons += 1;
+    const nth = teacher.nth(); // counted by slide.learn once the lesson is kept
     for (prompts.personal_prompts, 0..) |q, i| {
         if (try answeredByAny(srv, cx, told, kept, parts.own.items, q, document, gone)) continue;
         const reply = try ask(srv, cx, null, q, check_tokens, gone);
-        if (heldBack(teacher.lessons, i)) {
+        if (heldBack(nth, i)) {
             try checks.append(a, .{ .question = q, .before = reply.content });
             continue;
         }
@@ -156,14 +156,14 @@ pub fn lesson(srv: *Server, cx: *Cx, teacher: *Teacher, told: []const []const u8
             try stale_bank.append(a, i);
             continue;
         }
-        if ((i + teacher.lessons) % bank_checks == 0) try checks.append(a, .{ .question = b.question, .before = b.before }) else try keep.append(a, b.ex);
+        if ((i + nth) % bank_checks == 0) try checks.append(a, .{ .question = b.question, .before = b.before }) else try keep.append(a, b.ex);
     }
     // a fact in another language: its own language's prompts held and checked as the English ones are
     if (if (language) |name| try local(srv, cx, teacher, name, end, gone) else null) |l| {
         for (l.personal, 0..) |q, i| {
             if (try answeredByAny(srv, cx, told, kept, parts.own.items, q, document, gone)) continue;
             const reply = try ask(srv, cx, null, q, check_tokens, gone);
-            if (heldBack(teacher.lessons, i)) {
+            if (heldBack(nth, i)) {
                 try checks.append(a, .{ .question = q, .before = reply.content });
             } else try keep.append(a, try example(srv, cx, a, null, q, reply.content, ending(reply, end)));
         }
@@ -550,7 +550,7 @@ fn under(srv: *Server, cx: *Cx, head: api.Example, body: []const u32, r: Held) !
 }
 
 /// Whether personal prompt i is one this lesson asks again after it: three of them, turning with each lesson.
-fn heldBack(lessons: usize, i: usize) bool {
+pub fn heldBack(lessons: usize, i: usize) bool {
     const first = lessons * personal_checks % prompts.personal_prompts.len;
     return (i + prompts.personal_prompts.len - first) % prompts.personal_prompts.len < personal_checks;
 }
diff --git a/zig/src/server/slide_teacher.zig b/zig/src/server/slide_teacher.zig
index 85edf45988..03b5a0f39a 100644
--- a/zig/src/server/slide_teacher.zig
+++ b/zig/src/server/slide_teacher.zig
@@ -36,13 +36,23 @@ pub const Teacher = struct {
     turn_end: ?[]const u32 = null,
     thinks: ?bool = null, // whether the template opens the model's reasoning in its prompt
     languages: std.StringHashMapUnmanaged(Local) = .empty, // keep and personal prompts in each other language told so far
-    lessons: usize = 0, // lessons so far, which picks the questions about the user a check asks
+    lessons: usize = 0, // lessons kept so far, which picks the questions about the user a check asks
     told: std.ArrayList(Told) = .empty, // learned document facts' answers, which later lessons on their subject keep
 
     pub fn init(gpa: Allocator) Teacher {
         return .{ .arena = .init(gpa) };
     }
 
+    /// A lesson ended: kept, it counts; given up, the next lesson picks its checks as this one did (none of it stays).
+    pub fn ended(t: *Teacher, kept: bool) void {
+        if (kept) t.lessons += 1;
+    }
+
+    /// The number a lesson being written picks its checks by: one past the lessons kept.
+    pub fn nth(t: *const Teacher) usize {
+        return t.lessons + 1;
+    }
+
     /// A kept document lesson's held question and answer, by the subject its edit keys on (copied into the arena).
     pub fn remember(t: *Teacher, subject: []const u8, question: []const u8, answer: []const u8) !void {
         const a = t.arena.allocator();
diff --git a/zig/src/server/slide_teacher_test.zig b/zig/src/server/slide_teacher_test.zig
new file mode 100644
index 0000000000..6b2c70793d
--- /dev/null
+++ b/zig/src/server/slide_teacher_test.zig
@@ -0,0 +1,32 @@
+//! The teacher across lessons: a given-up lesson leaves the next kept lesson's checks as if it never ran.
+const std = @import("std");
+const lesson = @import("slide_lesson.zig");
+const prompts = @import("slide_prompts.zig");
+const Teacher = @import("slide_teacher.zig").Teacher;
+const testing = std.testing;
+
+/// The personal prompts a lesson numbered `nth` holds back to check (the rest it keeps as they are).
+fn checksOf(nth: usize) [prompts.personal_prompts.len]bool {
+    var out: [prompts.personal_prompts.len]bool = undefined;
+    for (&out, 0..) |*x, i| x.* = lesson.heldBack(nth, i);
+    return out;
+}
+
+test "a given-up lesson leaves the next kept lesson's checks as if it never ran" {
+    var t = Teacher.init(testing.allocator);
+    defer t.deinit();
+    var never = Teacher.init(testing.allocator); // the same lessons, the given-up one never tried
+    defer never.deinit();
+    const first = checksOf(t.nth());
+    try testing.expectEqualSlices(bool, &checksOf(never.nth()), &first);
+    t.ended(true);
+    never.ended(true);
+    const tried = t.nth(); // a lesson written, its rounds never bring the fact back, taken out
+    t.ended(false);
+    try testing.expectEqual(tried, t.nth()); // the next lesson writes as the given-up one did
+    const third = checksOf(t.nth());
+    try testing.expectEqualSlices(bool, &checksOf(never.nth()), &third);
+    try testing.expectEqual(@as(usize, 1), t.lessons);
+    // and the checks do turn with kept lessons (the held-back prompts differ from the first lesson's)
+    try testing.expect(!std.mem.eql(bool, &first, &third));
+}