diff --git a/apps/tests/phase129_if_only_post_if_return_var_min.hako b/apps/tests/phase129_if_only_post_if_return_var_min.hako
new file mode 100644
index 00000000..735392af
--- /dev/null
+++ b/apps/tests/phase129_if_only_post_if_return_var_min.hako
@@ -0,0 +1,22 @@
+// Phase 129: if-only post-if return var (Normalized join_k continuation)
+// Pattern: x=1; if flag==1 { x=2 }; return x
+// Expected: x=2 (flag=1 fixed)
+//
+// This tests that join_k continuation properly merges env:
+// - then: x=2 (updated)
+// - else: x=1 (original)
+// - join_k: receives env_phi and continues to return x
+
+static box Main {
+    main() {
+        local x
+        local flag
+        x = 1
+        flag = 1
+        if flag == 1 {
+            x = 2
+        }
+        print(x)
+        return "OK"
+    }
+}
diff --git a/docs/development/current/main/phases/phase-129/README.md b/docs/development/current/main/phases/phase-129/README.md
new file mode 100644
index 00000000..1620eb5b
--- /dev/null
+++ b/docs/development/current/main/phases/phase-129/README.md
@@ -0,0 +1,193 @@
+# Phase 129: Materialize join_k Continuation + LLVM Parity
+
+## Goal
+
+- Materialize join_k as a **real JoinFunction** (not just a concept)
+- Achieve VM+LLVM EXE parity for Phase 128 if-only partial assign pattern
+- Verify structural properties: join_k exists, PHI禁止 (no PHI in Normalized)
+
+## Background
+
+Phase 128 added basic Assign(int literal) support to Normalized builder, but:
+- join_k was mentioned in comments but not actually materialized
+- The If lowering doesn't generate a join continuation
+- post-if statements (e.g., `return x` after if) aren't supported in Normalized path
+
+Phase 129 fixes this by actually generating join_k as a JoinFunction.
+
+## Design
+
+### join_k Continuation Pattern
+
+```
+if cond {
+  x = 2  // then: env_then = env with x=2
+} else {
+  // else: env_else = env (unchanged)
+}
+print(x)  // post-if: needs env from both branches
+```
+
+**Normalized Lowering**:
+```
+then:
+  x = Const(2)
+  env_then[x] = new_vid
+  TailCall(join_k, env_then)
+
+else:
+  // no assignment
+  env_else = env (original)
+  TailCall(join_k, env_else)
+
+join_k(env_phi):
+  // env_phi is the merged environment
+  // post-if statements use env_phi
+  print(env_phi[x])
+  Ret
+```
+
+### Key Properties (SSOT)
+
+1. **join_k is a JoinFunction**: Not a concept, but actual function in JoinModule
+2. **then/else end with TailCall(join_k)**: Not Ret, not direct post-if
+3. **env merging is explicit**: env_phi parameter receives merged environment
+4. **PHI禁止**: No PHI instructions in Normalized (env update + continuation only)
+
+### Structural Verification
+
+`verify_normalized_structure()` enforces:
+- If node exists → join_k exists (as JoinFunction)
+- then/else don't end with Ret (they tail-call join_k)
+- join_k has env parameter (for merged environment)
+- No PHI instructions (structural check)
+
+## Scope
+
+### In-Scope (Phase 129)
+
+- If-only patterns (no loops)
+- Assign(int literal) RHS only (Phase 128 baseline)
+- post-if statements: print/return (minimal set)
+- VM + LLVM EXE parity (both must work)
+
+### Out-of-Scope
+
+- Loop patterns (Phase 130+)
+- Assign(complex expr) RHS (Phase 130+)
+- Nested if (Phase 130+)
+
+## Implementation Plan
+
+### P0: LLVM EXE smoke for Phase 128 ✅
+
+- Add `phase128_if_only_partial_assign_normalized_llvm_exe.sh`
+- Verify VM+LLVM parity for Phase 128 baseline
+- Regression: phase103, phase118
+
+**Status**: DONE (commit e7ad3d31b)
+
+### P1: Materialize join_k Continuation
+
+**Target**: `src/mir/control_tree/normalized_shadow/builder.rs`
+
+**Changes**:
+1. **lower_if_node**: Generate join_k function
+   - Create JoinFunction with env parameter
+   - then: `TailCall(join_k, env_then)`
+   - else: `TailCall(join_k, env_else)`
+   - join_k body: process post-if statements
+
+2. **verify_normalized_structure**: Add join_k checks
+   - If exists → join_k exists (by name or structure)
+   - then/else end with TailCall (not Ret)
+   - join_k has params (env fields)
+   - No PHI instructions anywhere
+
+**Acceptance**:
+- `cargo test --lib` PASS
+- Phase 128 VM smoke PASS
+- Phase 129 LLVM EXE smoke PASS (new fixture)
+
+### P2: Post-If Return Var Fixture
+
+**New fixture**: `apps/tests/phase129_if_only_post_if_return_var_min.hako`
+```hako
+x=1; flag=1; if flag==1 { x=2 }; print(x); return "OK"
+```
+
+**Expected**: `2` (x updated in then branch)
+
+**VM smoke**: `phase129_if_only_post_if_return_var_vm.sh`
+- `NYASH_JOINIR_DEV=1 HAKO_JOINIR_STRICT=1`
+- Verify join_k continuation works
+
+**Acceptance**:
+- VM smoke PASS
+- join_k actually used (not fallback path)
+
+### P3: Documentation
+
+- This README (DONE)
+- Update `10-Now.md` / `01-JoinIR-Selfhost-INDEX.md` / `30-Backlog.md`
+
+## Acceptance Criteria
+
+- ✅ P0: Phase 128 LLVM EXE smoke passes
+- [ ] P1: join_k materialized in builder.rs
+- [ ] P1: verify_normalized_structure enforces join_k properties
+- [ ] P2: Phase 129 fixture + VM smoke passes
+- [ ] P3: Documentation updated
+- [ ] Regression: phase103, phase118, phase128 all PASS
+- [ ] `cargo test --lib` PASS
+
+## Verification Commands
+
+```bash
+# Unit tests
+cargo test --lib
+
+# Smoke tests
+bash tools/smokes/v2/profiles/integration/apps/phase128_if_only_partial_assign_normalized_vm.sh
+bash tools/smokes/v2/profiles/integration/apps/phase128_if_only_partial_assign_normalized_llvm_exe.sh
+bash tools/smokes/v2/profiles/integration/apps/phase129_if_only_post_if_return_var_vm.sh
+
+# Regression
+bash tools/smokes/v2/profiles/integration/apps/phase103_if_only_llvm_exe.sh
+bash tools/smokes/v2/profiles/integration/apps/phase118_loop_nested_if_merge_vm.sh
+```
+
+## Feedback Points
+
+### Box-First Modularization
+
+- `lower_if_node`: Currently ~70 lines, could be split into:
+  - `generate_join_k_function` (create JoinFunction)
+  - `lower_if_branches` (then/else tail calls)
+  - Single responsibility principle
+
+### Fail-Fast Opportunities
+
+- verify_normalized_structure should fail early if:
+  - If exists but no join_k found
+  - then/else don't tail-call join_k
+  - join_k has no env parameter
+
+### Legacy Findings
+
+- Current `verify_branch_is_return_literal`: Too restrictive for Phase 129
+  - Should allow Assign statements in branches (Phase 128 already supports)
+  - Should verify tail-call to join_k (not just Return)
+
+## Related Phases
+
+- Phase 128: If-only partial assign (baseline)
+- Phase 113: If-only partial assign parity (StepTree path)
+- Phase 121-127: StepTree→Normalized foundation
+- Phase 130+: Loop patterns, complex RHS
+
+## Notes
+
+- **Dev-only**: `joinir_dev_enabled()` + `HAKO_JOINIR_STRICT=1` required
+- **PHI禁止**: Normalized path doesn't use PHI (env update + continuation instead)
+- **join_k naming**: Could use `join_k`, `k_join`, or auto-generate unique ID
diff --git a/tools/smokes/v2/profiles/integration/apps/phase129_if_only_post_if_return_var_vm.sh b/tools/smokes/v2/profiles/integration/apps/phase129_if_only_post_if_return_var_vm.sh
new file mode 100644
index 00000000..1fe4575f
--- /dev/null
+++ b/tools/smokes/v2/profiles/integration/apps/phase129_if_only_post_if_return_var_vm.sh
@@ -0,0 +1,63 @@
+#!/bin/bash
+# Phase 129: If-only Post-If Return Var (Normalized join_k, VM)
+#
+# Verifies that join_k continuation properly merges env after if:
+# - x=1; flag=1; if flag==1 { x=2 }; return x
+# - join_k receives env_phi (x=2 from then, x=1 from else)
+# - Returns x=2 (flag=1 fixed)
+# - Dev-only: NYASH_JOINIR_DEV=1 HAKO_JOINIR_STRICT=1
+
+source "$(dirname "$0")/../../../lib/test_runner.sh"
+source "$(dirname "$0")/../../../lib/output_validator.sh"
+export SMOKES_USE_PYVM=0
+require_env || exit 2
+
+PASS_COUNT=0
+FAIL_COUNT=0
+RUN_TIMEOUT_SECS=${RUN_TIMEOUT_SECS:-10}
+
+echo "[INFO] Phase 129: If-only Post-If Return Var (Normalized join_k, VM)"
+
+# Test 1: phase129_if_only_post_if_return_var_min.hako
+echo "[INFO] Test 1: phase129_if_only_post_if_return_var_min.hako"
+INPUT="$NYASH_ROOT/apps/tests/phase129_if_only_post_if_return_var_min.hako"
+
+set +e
+OUTPUT=$(timeout "$RUN_TIMEOUT_SECS" env \
+  NYASH_DISABLE_PLUGINS=1 \
+  HAKO_JOINIR_STRICT=1 \
+  NYASH_JOINIR_DEV=1 \
+  "$NYASH_BIN" --backend vm "$INPUT" 2>&1)
+EXIT_CODE=$?
+set -e
+
+if [ "$EXIT_CODE" -eq 124 ]; then
+  echo "[FAIL] hakorune timed out (>${RUN_TIMEOUT_SECS}s)"
+  FAIL_COUNT=$((FAIL_COUNT + 1))
+elif [ "$EXIT_CODE" -eq 0 ]; then
+  # Phase 129: expect x=2 (print(x) after if with x=2)
+  EXPECTED="2"
+  if validate_numeric_output 1 "$EXPECTED" "$OUTPUT"; then
+    echo "[PASS] Output verified: 2 (exit code: $EXIT_CODE)"
+    PASS_COUNT=$((PASS_COUNT + 1))
+  else
+    echo "[INFO] output (tail):"
+    echo "$OUTPUT" | tail -n 50 || true
+    FAIL_COUNT=$((FAIL_COUNT + 1))
+  fi
+else
+  echo "[FAIL] hakorune failed with exit code $EXIT_CODE"
+  echo "[INFO] output (tail):"
+  echo "$OUTPUT" | tail -n 50 || true
+  FAIL_COUNT=$((FAIL_COUNT + 1))
+fi
+
+echo "[INFO] PASS: $PASS_COUNT, FAIL: $FAIL_COUNT"
+
+if [ "$FAIL_COUNT" -eq 0 ]; then
+  test_pass "phase129_if_only_post_if_return_var_vm: All tests passed"
+  exit 0
+else
+  test_fail "phase129_if_only_post_if_return_var_vm: $FAIL_COUNT test(s) failed"
+  exit 1
+fi