diff --git a/docs/plans/2026-05-09-22c-user-class-e2e.md b/docs/plans/2026-05-09-22c-user-class-e2e.md
new file mode 100644
index 0000000..d5d073c
--- /dev/null
+++ b/docs/plans/2026-05-09-22c-user-class-e2e.md
@@ -0,0 +1,416 @@
+# 22c — User-class e2e fixture
+
+> **Parent spec:** `docs/specs/2026-05-09-22-typeclasses.md`
+>
+> **For agentic workers:** REQUIRED SUB-SKILL: use `skills/implement`
+> to run this plan. Steps use `- [ ]` checkboxes for tracking.
+
+**Goal:** ship one `.ail.json` fixture exercising the typeclass
+machinery end-to-end through user-defined code (no Prelude
+involvement). Running `ail build` on the fixture and executing the
+binary prints `42`.
+
+**Architecture:** the fixture defines a user class `Foo a` with one
+method, a user ADT `IntBox`, and an instance `Foo IntBox` whose body
+matches on the ctor and returns the wrapped int. `main` calls
+`foo (MkIntBox 42)` and prints the result through `io/print_int`. The
+22b.3 monomorphisation pass synthesises `foo__<typehash>` for
+`Foo IntBox`, rewrites the call site, and the existing match-lowering
+emits the body as ordinary code. No new compiler passes, no new
+runtime primitives, no new surface syntax.
+
+**Tech Stack:** `examples/` (one new fixture), `crates/ail/tests/`
+(one new e2e test file). No production-code crates touched.
+
+**Out of scope:** Prelude class for primitives (deferred per spec
+amendment 2026-05-09 §"22b.4b dropped"). Multiple instances per
+class, multi-method classes (`test_22b3_coherence_two_instances`
+and `test_22b3_default_e2e` already cover those).
+
+---
+
+## Files this plan creates or modifies
+
+- Create: `examples/test_22c_user_class_e2e.ail.json` — the fixture.
+- Create: `crates/ail/tests/typeclass_22c.rs` — the e2e test
+  (`cargo test -p ail --test typeclass_22c`). Asserts the binary
+  prints `42\n`.
+- Modify: `docs/JOURNAL.md` — append iteration entry at iter close.
+
+That is the entire iteration's surface. No code crate is modified,
+because 22b.3 already shipped every machine-code path the fixture
+exercises.
+
+---
+
+## Cross-task invariants
+
+1. **No production-code changes.** If a task requires editing
+   anything under `crates/*/src/` (other than tests), that is a
+   sign of a hidden bug surfaced by the fixture — STOP and route
+   through `debug` skill (RED-first), not through this plan.
+2. **No Prelude.** The fixture defines its own class; do NOT import
+   any `examples/prelude*.ail.json` (none exists yet anyway, but the
+   discipline matters: 22c's property is "user-defined" end-to-end).
+3. **Bench gates green.** Per spec acceptance criterion 2,
+   `bench/check.py` / `bench/compile_check.py` / `bench/cross_lang.py`
+   must all exit 0/0/0 at iter close.
+
+---
+
+## Task 1: Author the fixture
+
+**Files:**
+- Create: `examples/test_22c_user_class_e2e.ail.json`
+
+**Step 1.1 — Write the fixture**
+
+Hand-write the canonical JSON. Schema validation via `ail check`
+catches any shape error in Step 1.2. Key shapes verified against
+existing fixtures: `examples/box.ail.json` (data-type + match +
+term-ctor), `examples/test_22b3_default_e2e.ail.json` (class +
+instance with `(t: "lam")` body), `examples/borrow_own_demo.ail.json`
+(`param_modes: ["borrow"]` snake_case).
+
+```json
+{
+  "schema": "ailang/v0",
+  "name": "test_22c_user_class_e2e",
+  "imports": [],
+  "defs": [
+    {
+      "kind": "type",
+      "name": "IntBox",
+      "ctors": [
+        { "name": "MkIntBox", "fields": [{ "k": "con", "name": "Int" }] }
+      ]
+    },
+    {
+      "kind": "class",
+      "name": "Foo",
+      "param": "a",
+      "methods": [
+        {
+          "name": "foo",
+          "type": {
+            "k": "fn",
+            "params": [{ "k": "var", "name": "a" }],
+            "param_modes": ["borrow"],
+            "ret": { "k": "con", "name": "Int" },
+            "effects": []
+          }
+        }
+      ]
+    },
+    {
+      "kind": "instance",
+      "class": "Foo",
+      "type": { "k": "con", "name": "IntBox" },
+      "methods": [
+        {
+          "name": "foo",
+          "body": {
+            "t": "lam",
+            "params": ["b"],
+            "paramTypes": [{ "k": "var", "name": "a" }],
+            "retType": { "k": "con", "name": "Int" },
+            "body": {
+              "t": "match",
+              "scrutinee": { "t": "var", "name": "b" },
+              "arms": [
+                {
+                  "pat": {
+                    "p": "ctor",
+                    "ctor": "MkIntBox",
+                    "fields": [{ "p": "var", "name": "v" }]
+                  },
+                  "body": { "t": "var", "name": "v" }
+                }
+              ]
+            }
+          }
+        }
+      ]
+    },
+    {
+      "kind": "fn",
+      "name": "main",
+      "type": {
+        "k": "fn",
+        "params": [],
+        "ret": { "k": "con", "name": "Unit" },
+        "effects": ["IO"]
+      },
+      "params": [],
+      "body": {
+        "t": "do",
+        "op": "io/print_int",
+        "args": [
+          {
+            "t": "app",
+            "fn": { "t": "var", "name": "foo" },
+            "args": [
+              {
+                "t": "ctor",
+                "type": "IntBox",
+                "ctor": "MkIntBox",
+                "args": [{ "t": "lit", "lit": { "kind": "int", "value": 42 } }]
+              }
+            ]
+          }
+        ]
+      }
+    }
+  ]
+}
+```
+
+Notes on canonical key shape:
+- `data def: kind: "type"` (NOT `"data"`).
+- `Pattern: {"p": "ctor", ...}` / `{"p": "var", ...}` — discriminator
+  field is `"p"`, not `"pattern"` or `"kind"`. Pattern's child
+  patterns are under `"fields"`, not `"args"`.
+- `term-ctor: {"t": "ctor", "type": "IntBox", "ctor": "MkIntBox", "args": [...]}` —
+  the type name and the ctor name are sibling fields; do NOT use
+  `"t": "term-ctor"`.
+- Instance method body's `paramTypes` references the class param
+  variable `a` (not the concrete type `IntBox`). The mono pass
+  substitutes `a := IntBox` when synthesising the per-instance
+  function. Mirror the existing 22b.3 fixtures
+  (`test_22b3_coherence_two_instances` shows `paramTypes:
+  [{"k": "var", "name": "a"}]`).
+
+**Step 1.2 — Verify the fixture loads**
+
+```
+cargo run -q -p ail -- check examples/test_22c_user_class_e2e.ail.json
+```
+
+Expected: exit 0, no diagnostics.
+
+If `ail check` reports an error like `unknown method "foo"` or
+`no-instance for Foo IntBox`, that is a fixture bug — fix the JSON
+shape until check passes.
+
+If `ail check` reports an internal error or panics, STOP and route
+through `debug` skill RED-first — that is a real compiler bug
+surfaced by 22c, not a fixture issue.
+
+**Step 1.3 — Verify the fixture compiles and runs**
+
+```
+cargo run -q -p ail -- build examples/test_22c_user_class_e2e.ail.json -o /tmp/test_22c
+/tmp/test_22c
+```
+
+Expected: stdout `42\n`, exit 0.
+
+If `ail build` errors during monomorphisation / codegen / linking,
+STOP and route through `debug` skill — the fixture proves a real
+compiler-side gap (most likely candidates: mono pass on instance
+where the type is a user ADT, or match-lowering inside a synthesised
+mono fn).
+
+**Step 1.4 — Commit the fixture**
+
+```
+git add examples/test_22c_user_class_e2e.ail.json
+git commit -m "iter 22c.1: fixture — user class + user ADT + instance, prints 42"
+```
+
+---
+
+## Task 2: E2E test
+
+**Files:**
+- Create: `crates/ail/tests/typeclass_22c.rs`
+
+**Step 2.1 — Write the e2e test**
+
+Use the same shape as `crates/ail/tests/typeclass_22b3.rs`'s
+`synthetic_fixture_runs_and_prints_five` test (an existing precedent
+for "build + run a fixture and assert stdout"). Concretely:
+
+```rust
+//! Iter 22c: user-class end-to-end. The single 22c fixture defines a
+//! user class `Foo`, a user ADT `IntBox`, an `instance Foo IntBox`,
+//! and a `main` that calls `foo (MkIntBox 42)` through the
+//! monomorphisation pass and prints the result via `io/print_int`.
+//! This is the milestone-22 acceptance fixture for the user-class
+//! path (no Prelude involvement).
+
+use std::process::Command;
+
+fn workspace_root() -> std::path::PathBuf {
+    let manifest = std::path::PathBuf::from(env!("CARGO_MANIFEST_DIR"));
+    manifest.parent().unwrap().parent().unwrap().to_path_buf()
+}
+
+#[test]
+fn user_class_fixture_compiles_runs_and_prints_42() {
+    let root = workspace_root();
+    let fixture = root.join("examples/test_22c_user_class_e2e.ail.json");
+    let out = root.join("target/test-22c/test_22c");
+    std::fs::create_dir_all(out.parent().unwrap()).expect("mkdir");
+
+    // Build
+    let build = Command::new("cargo")
+        .args([
+            "run", "-q", "-p", "ail", "--",
+            "build", fixture.to_str().unwrap(),
+            "-o", out.to_str().unwrap(),
+        ])
+        .current_dir(&root)
+        .output()
+        .expect("spawn cargo run ail build");
+    assert!(
+        build.status.success(),
+        "ail build failed:\nstdout:\n{}\nstderr:\n{}",
+        String::from_utf8_lossy(&build.stdout),
+        String::from_utf8_lossy(&build.stderr)
+    );
+
+    // Run
+    let run = Command::new(&out)
+        .output()
+        .expect("spawn produced binary");
+    assert!(
+        run.status.success(),
+        "binary returned non-zero:\nstdout:\n{}\nstderr:\n{}",
+        String::from_utf8_lossy(&run.stdout),
+        String::from_utf8_lossy(&run.stderr)
+    );
+    assert_eq!(
+        String::from_utf8_lossy(&run.stdout).trim_end(),
+        "42",
+        "expected stdout `42` (with trailing newline)"
+    );
+}
+```
+
+If `crates/ail/tests/typeclass_22b3.rs` uses a different
+"build + run + capture stdout" idiom, mirror it instead — the
+project's existing convention takes priority over this template.
+
+**Step 2.2 — Run the test**
+
+```
+cargo test -p ail --test typeclass_22c
+```
+
+Expected: `1 passed; 0 failed`.
+
+**Step 2.3 — Run the full bench gate**
+
+```
+python3 bench/check.py
+python3 bench/compile_check.py
+python3 bench/cross_lang.py
+```
+
+Expected: all three exit 0/0/0.
+
+**Step 2.4 — Commit**
+
+```
+git add crates/ail/tests/typeclass_22c.rs
+git commit -m "iter 22c.2: e2e test — user-class fixture compiles, runs, prints 42"
+```
+
+---
+
+## Task 3: JOURNAL entry + milestone-close handoff
+
+**Files:**
+- Modify: `docs/JOURNAL.md` — append iteration entry.
+
+**Step 3.1 — Append the iteration entry**
+
+```markdown
+
+## 2026-05-09 — Iteration 22c: User-class e2e fixture
+
+The milestone-22 acceptance fixture for the user-class path. One new
+`examples/test_22c_user_class_e2e.ail.json` defines a user class
+`Foo a where foo : (a borrow) -> Int`, a user ADT `IntBox = MkIntBox
+Int`, an `instance Foo IntBox` whose body matches on the ctor and
+returns the wrapped int, and a `main` that calls `foo (MkIntBox 42)`
+through the 22b.3 monomorphisation pass and prints the result via
+`io/print_int`. Stdout: `42`.
+
+**Per-task subjects (mirror commit messages):**
+
+- 22c.1: fixture — user class + user ADT + instance, prints 42
+- 22c.2: e2e test — user-class fixture compiles, runs, prints 42
+
+**No production-code changes.** 22b.3 shipped every compiler path
+this fixture exercises (mono of class methods, call-site rewrite,
+synthesised symbol naming via `__` separator, match lowering inside
+synthesised bodies). The fact that 22c lands as a pure-fixture iter
+is the strongest possible evidence that the typeclass machinery is
+done — there is nothing left to wire.
+
+**Spec amendments folded into 22b.4a's amendment block:**
+22b.4b (Prelude for primitives) dropped from milestone scope; 22c's
+fixture re-scoped to vocabulary AILang already has (no `++`, no
+named-field record syntax, no top-level polymorphic `print`). See
+`docs/specs/2026-05-09-22-typeclasses.md` "Amendments" §"22b.4b
+dropped" and §"22c scope tightened".
+
+**Milestone-22 acceptance check:**
+
+1. ✓ 22b.1 + 22b.2 + 22b.3 + 22b.4a + 22c JOURNAL entries committed.
+2. (pending) Audit suite green — `audit` skill runs next.
+3. ✓ 22c user-class fixture compiles, runs, prints `42` (this iter).
+4. ✓ Round-trip filter retired in 22b.4a; all `examples/*.ail.json`
+   pass round-trip.
+
+**Bench gates:** all three exited 0/0/0.
+
+**Next step:** dispatch `audit` skill to close the milestone —
+architect drift review against `docs/DESIGN.md` plus the three
+regression scripts (already 0/0/0 here but `audit` re-runs as
+its own gate). On clean audit: milestone 22 closes; queue moves
+to whatever's next. On drift: tidy iteration first.
+```
+
+**Step 3.2 — Commit**
+
+```
+git add docs/JOURNAL.md
+git commit -m "iter 22c: journal entry — milestone-22 acceptance fixture lands"
+```
+
+---
+
+## Acceptance gate (run after Task 3)
+
+```
+cargo test --workspace
+python3 bench/check.py
+python3 bench/compile_check.py
+python3 bench/cross_lang.py
+```
+
+All four green is the iteration close. The orchestrator then
+dispatches `skills/audit` to close milestone 22.
+
+---
+
+## Self-review checklist (orchestrator, pre-commit)
+
+1. **Spec coverage:** every spec acceptance criterion has a task
+   that satisfies it. Criterion 1 (JOURNAL) → Task 3; Criterion 3
+   (22c fixture compiles + runs) → Tasks 1+2; Criterion 4 (round-trip)
+   → already satisfied by 22b.4a. ✓
+2. **Placeholder scan:** grep this file for "TBD" / "TODO" / "fill
+   in" / "implement later" / "similar to" / "add appropriate". Zero
+   hits. ✓
+3. **Type consistency:** the fixture's class name, method name, ADT
+   name, ctor name, instance binding, and main call site all use
+   `Foo` / `foo` / `IntBox` / `MkIntBox` consistently. ✓
+4. **Step granularity:** every step ≤ 5 minutes. The two ambiguous
+   steps are 1.2 and 1.3 (verify check + verify build) — they may
+   surface compiler bugs that aren't 5-minute fixes. The plan
+   instructs STOP and route to `debug` in that case, which is the
+   right discipline. ✓