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+# schema-camelcase-fix — Implementation Plan
+
+> **Parent spec:** `docs/specs/2026-05-21-schema-camelcase-fix.md`
+> (commit `55ce6d0`, amended after plan-recon)
+>
+> **For agentic workers:** REQUIRED SUB-SKILL: use `skills/implement`
+> to run this plan. Steps use `- [ ]` checkboxes for tracking.
+
+**Goal:** Rename the two camelCase JSON tags `paramTypes` / `retType`
+on `Term::Lam` to the kebab-case `param-types` / `ret-type`,
+migrate every checked-in code/contract reference in the same
+iteration, and pin the new schema shape with a `design_schema_drift`
+assertion. After this iteration the AILang canonical-JSON schema
+has zero camelCase tags. Closes Gitea #30.
+
+**Architecture:** Single-iteration milestone. Four layers
+touched: (1) `#[serde(rename)]` strings on `Term::Lam` in
+`crates/ailang-core/src/ast.rs`; (2) one in-source test JSON-literal
+in `crates/ailang-core/src/workspace.rs`; (3) two `.ail.json` fixtures
++ one canonical-schema contract document
+(`design/contracts/data-model.md`); (4) three rustdoc strings that
+describe present-state schema vocabulary. The Form-A surface
+(`crates/ailang-surface/`) is structurally untouched — Form-A uses
+`(params (typed ...)) (ret ...)`, not the renamed tags. No hash-pin
+refresh is required (no `.ail` module currently pinned in
+`hash_pin.rs` contains a `(lam ...)` term — verified per-file).
+
+**Tech Stack:** `serde_json` rename attributes, AILang `Term::Lam`
+schema, `design_schema_drift.rs` anchor walker, `anchor_in_jsonc_block`
+helper.
+
+---
+
+## Files this plan creates or modifies
+
+- Modify: `crates/ailang-core/tests/design_schema_drift.rs` — add
+  one new `#[test] fn` (the schema-shape pin) and extend the
+  existing `anchor_in_jsonc_block` walk to require the new tag
+  spellings inside the `Term::Lam` fenced JSON block of
+  `data-model.md`.
+- Modify: `crates/ailang-core/src/ast.rs:492,494` — two
+  `#[serde(rename)]` string-literal swaps.
+- Modify: `crates/ailang-core/src/ast.rs:8` — module-level `//!`
+  rustdoc enumerates rename targets.
+- Modify: `crates/ailang-core/src/workspace.rs:1925-1926` — in-source
+  JSON literal inside `#[test] fn ct1_validator_walks_lam_embedded_types`
+  (function at line 1911).
+- Modify: `crates/ailang-surface/src/parse.rs:81` — module-level
+  `//!` rustdoc mentions `lam`'s `paramTypes` carry.
+- Modify: `crates/ailang-check/src/lib.rs:1707` — `///` rustdoc on
+  the InstanceMethod routing helper.
+- Modify: `design/contracts/data-model.md:142-147` — fenced JSON
+  block describing the `Term::Lam` schema.
+- Modify: `examples/test_loop_binder_captured_by_lambda.ail.json`
+  — two key renames, one per line (currently lines 32-33; verify
+  by grep before editing).
+- Modify: `experiments/2026-05-12-cross-model-authoring/master/examples/fn_with_lambda.ail.json`
+  — two key renames, one per line (currently lines 25-26).
+
+**Forbidden touches** (per spec acceptance criterion 7):
+- `docs/plans/2026-05-10-23.3-*.md`, `docs/plans/2026-05-09-22b3-monomorphisation.md`,
+  `docs/plans/2026-05-09-22c-user-class-e2e.md`, `docs/plans/24.2.md`
+- `experiments/2026-05-12-cross-model-authoring/master/spec.md`
+- `experiments/2026-05-12-cross-model-authoring/rendered/*.md`
+- `experiments/2026-05-12-cross-model-authoring/runs/**`
+
+These embed the old tag names but are frozen historical artefacts.
+
+---
+
+## Task 1: RED — pin the new schema shape
+
+**Files:**
+- Modify: `crates/ailang-core/tests/design_schema_drift.rs`
+
+The pin lives in `design_schema_drift.rs` (not `schema_coverage.rs`)
+because that file already constructs `Term::Lam` exemplars at
+L121-129, already includes `data-model.md` via `include_str!`
+(L22, constant name `DATA_MODEL`), and already calls the
+`anchor_in_jsonc_block` helper (L34-47, called at L184) for fenced-
+block walks. The new pin and the data-model anchor extension belong
+in the same test file as the rest of the schema-drift family.
+
+- [ ] **Step 1: Read the existing pin family**
+
+Read `crates/ailang-core/tests/design_schema_drift.rs`. Note:
+- the `Term::Lam` exemplar around L121-129
+- the `anchor_in_jsonc_block` helper at L34-47
+- the existing `design_md_anchors_every_term_variant` test (where
+  the new tag anchors will land)
+
+Step exists to ground the new test in the file's prevailing shape;
+no edit.
+
+- [ ] **Step 2: Add the schema-shape pin**
+
+Append at end of `crates/ailang-core/tests/design_schema_drift.rs`
+(or co-locate with the other `Term::Lam`-touching tests at L121-129
+— pick the location with the closest sibling test):
+
+```rust
+/// Schema-shape pin: the JSON serialisation of `Term::Lam` must
+/// emit kebab-case tags `"param-types"` and `"ret-type"`, and
+/// must NOT emit the old camelCase `"paramTypes"` / `"retType"`.
+/// Pinned because the closes-#30 milestone made the rename a
+/// schema-stability invariant: a future regression that flips
+/// the `#[serde(rename)]` string back to camelCase must fire RED
+/// here, not slip through.
+#[test]
+fn lam_serialises_with_kebab_keys() {
+    use ailang_core::ast::*;
+
+    let lam = Term::Lam {
+        params: vec!["x".into()],
+        param_tys: vec![Type::int()],
+        ret_ty: Box::new(Type::int()),
+        effects: vec![],
+        body: Box::new(Term::Var { name: "x".into() }),
+    };
+    let v = serde_json::to_value(&lam).expect("Term::Lam serialises");
+    let obj = v.as_object().expect("Term::Lam serialises as object");
+
+    assert!(
+        obj.contains_key("param-types"),
+        "Term::Lam must emit `param-types` key; got keys {:?}",
+        obj.keys().collect::<Vec<_>>(),
+    );
+    assert!(
+        obj.contains_key("ret-type"),
+        "Term::Lam must emit `ret-type` key; got keys {:?}",
+        obj.keys().collect::<Vec<_>>(),
+    );
+    assert!(
+        !obj.contains_key("paramTypes"),
+        "Term::Lam must NOT emit old camelCase `paramTypes` key",
+    );
+    assert!(
+        !obj.contains_key("retType"),
+        "Term::Lam must NOT emit old camelCase `retType` key",
+    );
+}
+```
+
+- [ ] **Step 3: Extend the data-model.md anchor walk**
+
+Find the existing test that uses `anchor_in_jsonc_block` to assert
+fenced-block content (recon names `design_md_anchors_every_term_variant`
+at the test name level, and `anchor_in_jsonc_block` calls at L184).
+Read the existing anchor list, identify where the `lam` block
+anchors live, and add two new anchor assertions for the same `lam`
+fenced JSON block:
+
+```rust
+assert!(
+    anchor_in_jsonc_block(DATA_MODEL, "lam", "\"param-types\""),
+    "data-model.md `lam` fenced block must list `param-types` key",
+);
+assert!(
+    anchor_in_jsonc_block(DATA_MODEL, "lam", "\"ret-type\""),
+    "data-model.md `lam` fenced block must list `ret-type` key",
+);
+```
+
+If the existing test asserts anchors via a `for (variant, anchor) in &[…]` table, add the two rows there instead of two
+standalone `assert!`s — match the local shape. The implementer
+reads the file to confirm the local shape before editing.
+
+- [ ] **Step 4: Run the new pin and verify it FAILS**
+
+Run: `cargo test -p ailang-core --test design_schema_drift lam_serialises_with_kebab_keys 2>&1 | tail -30`
+
+Expected: FAIL. The current `ast.rs:492,494` emit `paramTypes` /
+`retType`, so `obj.contains_key("param-types")` is false. The
+data-model anchor extension also FAILs because lines 142-147 still
+carry camelCase. Both RED conditions confirm we are pinning a real
+property the milestone is about to make true.
+
+If the test unexpectedly passes, STOP — the assumption "current
+state emits camelCase" is wrong; re-read `ast.rs:490-499` before
+proceeding.
+
+---
+
+## Task 2: GREEN-1 — atomic schema-coupled swap
+
+**Files:**
+- Modify: `crates/ailang-core/src/ast.rs:492` (line `#[serde(rename = "paramTypes")]`)
+- Modify: `crates/ailang-core/src/ast.rs:494` (line `#[serde(rename = "retType")]`)
+- Modify: `crates/ailang-core/src/workspace.rs:1925-1926`
+- Modify: `examples/test_loop_binder_captured_by_lambda.ail.json`
+- Modify: `experiments/2026-05-12-cross-model-authoring/master/examples/fn_with_lambda.ail.json`
+- Modify: `design/contracts/data-model.md:142-147`
+
+These files MUST move together. Changing only `ast.rs` makes any
+JSON literal containing the old tags undeserialisable: serde
+`Term::Lam` has no `#[serde(default)]` on `param_tys` / `ret_ty`,
+so an absent (renamed-away) key is a hard deserialise error. The
+workspace.rs test, the two `.ail.json` fixtures, and the
+data-model.md fenced JSON block all participate in the same
+serialiser/deserialiser contract — they migrate atomically, in a
+single task, with the full `cargo test` gate at the end.
+
+`data-model.md` is included by `data-model.md` consumer
+`design_schema_drift.rs` via `include_str!`; the constant is
+`DATA_MODEL`. After Task 1's anchor extension, leaving the fenced
+JSON block on camelCase would keep the test RED.
+
+- [ ] **Step 1: Edit `crates/ailang-core/src/ast.rs:492`**
+
+Locate line 492:
+
+```rust
+        #[serde(rename = "paramTypes")]
+```
+
+Replace with:
+
+```rust
+        #[serde(rename = "param-types")]
+```
+
+- [ ] **Step 2: Edit `crates/ailang-core/src/ast.rs:494`**
+
+Locate line 494:
+
+```rust
+        #[serde(rename = "retType")]
+```
+
+Replace with:
+
+```rust
+        #[serde(rename = "ret-type")]
+```
+
+- [ ] **Step 3: Edit `crates/ailang-core/src/workspace.rs:1925-1926`**
+
+The two lines live inside the test function
+`ct1_validator_walks_lam_embedded_types` (function attribute `#[test]`
+at L1911). Find the literal lines:
+
+```rust
+                    "paramTypes": [{ "k": "con", "name": "Ordering" }],
+                    "retType": { "k": "con", "name": "Unit" },
+```
+
+Replace with (preserve exact indentation and surrounding context):
+
+```rust
+                    "param-types": [{ "k": "con", "name": "Ordering" }],
+                    "ret-type": { "k": "con", "name": "Unit" },
+```
+
+- [ ] **Step 4: Edit `examples/test_loop_binder_captured_by_lambda.ail.json`**
+
+Grep first to confirm exact occurrences:
+
+Run: `grep -n '"paramTypes"\|"retType"' examples/test_loop_binder_captured_by_lambda.ail.json`
+
+Expected: 2 hits, one with `"paramTypes"`, one with `"retType"`,
+on consecutive lines (currently 32-33; verify).
+
+For each line, replace `"paramTypes"` → `"param-types"` and
+`"retType"` → `"ret-type"`. No other content changes.
+
+- [ ] **Step 5: Edit `experiments/2026-05-12-cross-model-authoring/master/examples/fn_with_lambda.ail.json`**
+
+Grep first:
+
+Run: `grep -n '"paramTypes"\|"retType"' experiments/2026-05-12-cross-model-authoring/master/examples/fn_with_lambda.ail.json`
+
+Expected: 2 hits on consecutive lines (currently 25-26; verify).
+
+Same rename as Step 4.
+
+- [ ] **Step 6: Edit `design/contracts/data-model.md:142-147`**
+
+The fenced JSON block currently reads (lines 142-147):
+
+```
+{ "t": "lam",
+  "params": ["<id>"...],
+  "paramTypes": [Type...],
+  "retType": Type,
+  "effects": ["<id>"...],
+  "body": Term }
+```
+
+Replace lines 144-145 with:
+
+```
+  "param-types": [Type...],
+  "ret-type": Type,
+```
+
+The surrounding `{ "t": "lam", ...` opener, `"params"` line,
+`"effects"` line, and `"body"` line are untouched. Verify the
+fenced-block boundaries (` ``` ` markers) above and below remain
+intact.
+
+- [ ] **Step 7: Build the workspace to catch any deserialisation regression**
+
+Run: `cargo build --workspace 2>&1 | tail -20`
+
+Expected: clean build, no new warnings.
+
+- [ ] **Step 8: Run the schema-shape pin (now expected GREEN)**
+
+Run: `cargo test -p ailang-core --test design_schema_drift lam_serialises_with_kebab_keys 2>&1 | tail -10`
+
+Expected: PASS (Task 1's assertion now holds).
+
+- [ ] **Step 9: Run the extended data-model anchor walk**
+
+Run: `cargo test -p ailang-core --test design_schema_drift design_md_anchors_every_term_variant 2>&1 | tail -10`
+
+Expected: PASS (the data-model.md fenced JSON block now carries
+the new tag anchors).
+
+- [ ] **Step 10: Run the workspace ct1 test**
+
+Run: `cargo test -p ailang-core ct1_validator_walks_lam_embedded_types 2>&1 | tail -10`
+
+Expected: PASS. This is the in-source test that owns the JSON
+literal edited in Step 3; if Step 3 missed a key, this test fails
+with a `serde_json::from_value` error mentioning the missing field.
+
+---
+
+## Task 3: GREEN-2 — rustdoc honesty pass
+
+**Files:**
+- Modify: `crates/ailang-core/src/ast.rs:8`
+- Modify: `crates/ailang-surface/src/parse.rs:81`
+- Modify: `crates/ailang-check/src/lib.rs:1707`
+
+These are pure prose edits — no compile or test consequence. They
+exist solely to keep the rustdoc honest after the rename. Per the
+Honesty Rule (`design/contracts/honesty-rule.md`), production
+rustdoc describes present-state vocabulary, not history.
+
+- [ ] **Step 1: Edit `crates/ailang-core/src/ast.rs:8`**
+
+Locate line 8 in the module-level `//!` block. Current text:
+
+```rust
+//! `fn`, `paramTypes`, `retType`), enum tags (`kind`, `t`, `k`, `p`),
+```
+
+Replace with:
+
+```rust
+//! `fn`, `param-types`, `ret-type`), enum tags (`kind`, `t`, `k`, `p`),
+```
+
+The surrounding `//!` lines are untouched.
+
+- [ ] **Step 2: Edit `crates/ailang-surface/src/parse.rs:81`**
+
+Locate line 81 in the module-level `//!` block. Current text:
+
+```rust
+//! - The `lam` form carries `paramTypes`, a `ret` type, and an
+```
+
+Replace with:
+
+```rust
+//! - The `lam` form carries `param-types`, a `ret` type, and an
+```
+
+If the line wraps differently in the local file (the carrier word
+`paramTypes` may sit on its own line or break across lines after
+the comma), edit the contiguous `paramTypes` occurrence; do NOT
+soft-wrap split the new `param-types` across two lines.
+
+- [ ] **Step 3: Edit `crates/ailang-check/src/lib.rs:1707`**
+
+Locate line 1707. Current text:
+
+```rust
+/// convention a `Term::Lam` carrying its own `paramTypes` / `retType`
+```
+
+Replace with:
+
+```rust
+/// convention a `Term::Lam` carrying its own `param-types` / `ret-type`
+```
+
+- [ ] **Step 4: Run a doc-build to catch broken intra-doc links**
+
+Run: `cargo doc --workspace --no-deps 2>&1 | grep -E "warning|error" | head -20`
+
+Expected: no NEW warnings (the workspace already carries a
+known-stable warning count; flag any new diagnostic that mentions
+`paramTypes` / `retType` / `param-types` / `ret-type`).
+
+---
+
+## Task 4: Final verification
+
+**Files:** none modified — verification only.
+
+- [ ] **Step 1: Exhaustive grep — nothing left on the old tags**
+
+Run: `grep -rn '"paramTypes"\|"retType"\|paramTypes\|retType' crates/ examples/ design/ runtime/ --include='*.rs' --include='*.json' --include='*.md' 2>/dev/null`
+
+Expected output (and only this output):
+- `docs/plans/*.md` matches in the historic plan files listed under "Forbidden touches" above.
+- `experiments/2026-05-12-cross-model-authoring/master/spec.md` matches.
+- `experiments/2026-05-12-cross-model-authoring/rendered/*.md` matches.
+- `experiments/2026-05-12-cross-model-authoring/runs/**` matches.
+- ZERO matches under `crates/`, `examples/`, `runtime/`, or `design/`.
+
+Any match outside the expected set is a missed touch-point; resolve
+it by adding the rename, then re-run the full test suite (Step 2).
+
+- [ ] **Step 2: Run the workspace test suite**
+
+Run: `cargo test --workspace 2>&1 | tail -25`
+
+Expected: every crate's test summary shows `0 failed`. The total
+test-group count must equal the pre-iter baseline of 90
+(unchanged — Task 1 adds one new test inside an existing test crate,
+which does not change the test-group count).
+
+- [ ] **Step 3: Round-trip invariance check**
+
+Run: `cargo test -p ailang-surface --test round_trip 2>&1 | tail -10`
+
+Expected: PASS. This is the Form-A-unchanged gate; if it fails
+the spec's Layer-2 claim ("Form-A never used these tag names") was
+wrong and the iteration scope was mis-sized.
+
+- [ ] **Step 4: Confirm no forbidden files were touched**
+
+Run: `git diff --name-only HEAD 2>&1 | grep -E "docs/plans/|experiments/.*/(master/spec\.md|rendered/|runs/)" | head -20`
+
+Expected: empty output. If any line appears, the implementer
+mutated a forbidden file — `git checkout -- <path>` the change.
+
+- [ ] **Step 5: Sanity check the new pin would actually go RED**
+
+Mental check (no `git revert` — main is sacrosanct): the pin in
+Task 1 was confirmed RED in Task 1 Step 4 before the swap. Step 8
+of Task 2 confirmed it GREEN after the swap. Therefore the pin is
+a real RED/GREEN bisector. No additional action — this step exists
+to mark the property as audited.
+
+- [ ] **Step 6: Status summary for Boss commit**
+
+Print a one-line summary of the resulting `git status`:
+
+Run: `git status --short`
+
+Expected: nine modified files (the eight listed in "Files this
+plan creates or modifies" plus the new test slot in
+`design_schema_drift.rs`), no untracked files of interest. The
+Boss will inspect the diff and assemble the iter-level commit.