diff --git a/.gitattributes b/.gitattributes
new file mode 100644
index 0000000..00657cd
--- /dev/null
+++ b/.gitattributes
@@ -0,0 +1,2 @@
+conformance/invalid/byte-order-mark/source.stack binary
+conformance/invalid/invalid-utf8/source.stack binary
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index af7a038..96721a9 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -49,3 +49,6 @@ jobs:
 
       - name: Validate diagnostic fixtures
         run: find conformance -name expected.diagnostics.json -print0 | xargs -0 check-jsonschema --schemafile schemas/diagnostic-expectations.schema.json
+
+      - name: Validate compiler diagnostic coverage
+        run: python scripts/validate-compiler-diagnostics.py
diff --git a/README.md b/README.md
index f5db645..5c067cf 100644
--- a/README.md
+++ b/README.md
@@ -61,6 +61,7 @@ python -m pip install --requirement requirements-dev.txt
 check-jsonschema --check-metaschema schemas/*.json
 check-jsonschema --schemafile schemas/normalized-ir.schema.json conformance/valid/*/expected.ir.json
 find conformance -name expected.diagnostics.json -print0 | xargs -0 check-jsonschema --schemafile schemas/diagnostic-expectations.schema.json
+python scripts/validate-compiler-diagnostics.py
 ```
 
 ## Design Principles
diff --git a/conformance/README.md b/conformance/README.md
index 0c275e8..0fca87b 100644
--- a/conformance/README.md
+++ b/conformance/README.md
@@ -19,6 +19,10 @@ invalid/<case-id>/expected.diagnostics.json
 
 Expected IR documents conform to [`normalized-ir.schema.json`](../schemas/normalized-ir.schema.json). Diagnostic expectation documents conform to [`diagnostic-expectations.schema.json`](../schemas/diagnostic-expectations.schema.json).
 
+The canonical suite covers every Stack 1.0 diagnostic assigned to compiler stages 1 through 4: `STK1001` through `STK3014`, excluding unassigned numbers, plus `STK4002` and `STK4003`. [`validate-compiler-diagnostics.py`](../scripts/validate-compiler-diagnostics.py) verifies that every required code occurs in at least one expectation document. Renderer-stage `STK4001`, `STK5001`, and `STK6001` remain outside compiler conformance.
+
+The encoding cases intentionally include raw invalid UTF-8, a UTF-8 byte order mark, CRLF line endings, and a Unicode scalar before an error position. Tools must preserve `source.stack` bytes rather than decoding and rewriting fixtures during discovery.
+
 ## Comparison
 
 - JSON values are compared semantically; formatting and object-member order do not matter.
diff --git a/conformance/invalid/byte-order-mark/expected.diagnostics.json b/conformance/invalid/byte-order-mark/expected.diagnostics.json
new file mode 100644
index 0000000..9c4b3b5
--- /dev/null
+++ b/conformance/invalid/byte-order-mark/expected.diagnostics.json
@@ -0,0 +1,13 @@
+{
+  "schemaVersion": "1.0",
+  "diagnostics": [
+    {
+      "code": "STK1002",
+      "severity": "error",
+      "range": {
+        "start": { "byteOffset": 0, "line": 1, "column": 1 },
+        "end": { "byteOffset": 3, "line": 1, "column": 2 }
+      }
+    }
+  ]
+}
diff --git a/conformance/invalid/byte-order-mark/source.stack b/conformance/invalid/byte-order-mark/source.stack
new file mode 100644
index 0000000..d020a50
--- /dev/null
+++ b/conformance/invalid/byte-order-mark/source.stack
@@ -0,0 +1,4 @@
+stack 1.0
+diagram "BOM" {
+  node api "API"
+}
diff --git a/conformance/invalid/duplicate-theme-dense-node/expected.diagnostics.json b/conformance/invalid/duplicate-theme-dense-node/expected.diagnostics.json
new file mode 100644
index 0000000..1a3381f
--- /dev/null
+++ b/conformance/invalid/duplicate-theme-dense-node/expected.diagnostics.json
@@ -0,0 +1,21 @@
+{
+  "schemaVersion": "1.0",
+  "diagnostics": [
+    {
+      "code": "STK3014",
+      "severity": "error",
+      "range": {
+        "start": { "byteOffset": 44, "line": 4, "column": 3 },
+        "end": { "byteOffset": 54, "line": 4, "column": 13 }
+      }
+    },
+    {
+      "code": "STK4002",
+      "severity": "warning",
+      "range": {
+        "start": { "byteOffset": 62, "line": 5, "column": 8 },
+        "end": { "byteOffset": 65, "line": 5, "column": 11 }
+      }
+    }
+  ]
+}
diff --git a/conformance/invalid/duplicate-theme-dense-node/source.stack b/conformance/invalid/duplicate-theme-dense-node/source.stack
new file mode 100644
index 0000000..f1e153c
--- /dev/null
+++ b/conformance/invalid/duplicate-theme-dense-node/source.stack
@@ -0,0 +1,32 @@
+stack 1.0
+diagram "Dense" {
+  theme light
+  theme dark
+  node hub "Hub"
+  node n0 "N 0"
+  node n1 "N 1"
+  node n2 "N 2"
+  node n3 "N 3"
+  node n4 "N 4"
+  node n5 "N 5"
+  node n6 "N 6"
+  node n7 "N 7"
+  node n8 "N 8"
+  node n9 "N 9"
+  node n10 "N 10"
+  node n11 "N 11"
+  node n12 "N 12"
+  edge hub -> n0
+  edge hub -> n1
+  edge hub -> n2
+  edge hub -> n3
+  edge hub -> n4
+  edge hub -> n5
+  edge hub -> n6
+  edge hub -> n7
+  edge hub -> n8
+  edge hub -> n9
+  edge hub -> n10
+  edge hub -> n11
+  edge hub -> n12
+}
diff --git a/conformance/invalid/edge-rules/expected.diagnostics.json b/conformance/invalid/edge-rules/expected.diagnostics.json
new file mode 100644
index 0000000..c63e800
--- /dev/null
+++ b/conformance/invalid/edge-rules/expected.diagnostics.json
@@ -0,0 +1,29 @@
+{
+  "schemaVersion": "1.0",
+  "diagnostics": [
+    {
+      "code": "STK3007",
+      "severity": "error",
+      "range": {
+        "start": { "byteOffset": 61, "line": 3, "column": 34 },
+        "end": { "byteOffset": 67, "line": 3, "column": 40 }
+      }
+    },
+    {
+      "code": "STK3005",
+      "severity": "error",
+      "range": {
+        "start": { "byteOffset": 85, "line": 5, "column": 3 },
+        "end": { "byteOffset": 96, "line": 5, "column": 14 }
+      }
+    },
+    {
+      "code": "STK3006",
+      "severity": "error",
+      "range": {
+        "start": { "byteOffset": 113, "line": 7, "column": 3 },
+        "end": { "byteOffset": 124, "line": 7, "column": 14 }
+      }
+    }
+  ]
+}
diff --git a/conformance/invalid/edge-rules/source.stack b/conformance/invalid/edge-rules/source.stack
new file mode 100644
index 0000000..ef48811
--- /dev/null
+++ b/conformance/invalid/edge-rules/source.stack
@@ -0,0 +1,8 @@
+stack 1.0
+diagram "Edges" {
+  node a "A" { kind service kind worker }
+  node b "B"
+  edge a -> a
+  edge a -- b
+  edge b -- a
+}
diff --git a/conformance/invalid/empty-diagram/expected.diagnostics.json b/conformance/invalid/empty-diagram/expected.diagnostics.json
new file mode 100644
index 0000000..252472c
--- /dev/null
+++ b/conformance/invalid/empty-diagram/expected.diagnostics.json
@@ -0,0 +1,13 @@
+{
+  "schemaVersion": "1.0",
+  "diagnostics": [
+    {
+      "code": "STK4003",
+      "severity": "error",
+      "range": {
+        "start": { "byteOffset": 10, "line": 2, "column": 1 },
+        "end": { "byteOffset": 28, "line": 2, "column": 19 }
+      }
+    }
+  ]
+}
diff --git a/conformance/invalid/empty-diagram/source.stack b/conformance/invalid/empty-diagram/source.stack
new file mode 100644
index 0000000..16f68a4
--- /dev/null
+++ b/conformance/invalid/empty-diagram/source.stack
@@ -0,0 +1,2 @@
+stack 1.0
+diagram "Empty" {}
diff --git a/conformance/invalid/independent-semantic-errors/expected.diagnostics.json b/conformance/invalid/independent-semantic-errors/expected.diagnostics.json
new file mode 100644
index 0000000..1acece6
--- /dev/null
+++ b/conformance/invalid/independent-semantic-errors/expected.diagnostics.json
@@ -0,0 +1,77 @@
+{
+  "schemaVersion": "1.0",
+  "diagnostics": [
+    {
+      "code": "STK2001",
+      "severity": "error",
+      "range": {
+        "start": { "byteOffset": 0, "line": 1, "column": 1 },
+        "end": { "byteOffset": 9, "line": 1, "column": 10 }
+      }
+    },
+    {
+      "code": "STK3008",
+      "severity": "error",
+      "range": {
+        "start": { "byteOffset": 18, "line": 2, "column": 9 },
+        "end": { "byteOffset": 25, "line": 2, "column": 16 }
+      }
+    },
+    {
+      "code": "STK3009",
+      "severity": "error",
+      "range": {
+        "start": { "byteOffset": 36, "line": 3, "column": 9 },
+        "end": { "byteOffset": 41, "line": 3, "column": 14 }
+      }
+    },
+    {
+      "code": "STK3001",
+      "severity": "error",
+      "range": {
+        "start": { "byteOffset": 60, "line": 4, "column": 8 },
+        "end": { "byteOffset": 63, "line": 4, "column": 11 }
+      }
+    },
+    {
+      "code": "STK3008",
+      "severity": "error",
+      "range": {
+        "start": { "byteOffset": 64, "line": 4, "column": 12 },
+        "end": { "byteOffset": 66, "line": 4, "column": 14 }
+      }
+    },
+    {
+      "code": "STK3001",
+      "severity": "error",
+      "range": {
+        "start": { "byteOffset": 74, "line": 5, "column": 8 },
+        "end": { "byteOffset": 77, "line": 5, "column": 11 }
+      }
+    },
+    {
+      "code": "STK3002",
+      "severity": "error",
+      "range": {
+        "start": { "byteOffset": 74, "line": 5, "column": 8 },
+        "end": { "byteOffset": 77, "line": 5, "column": 11 }
+      }
+    },
+    {
+      "code": "STK3003",
+      "severity": "error",
+      "range": {
+        "start": { "byteOffset": 97, "line": 6, "column": 8 },
+        "end": { "byteOffset": 104, "line": 6, "column": 15 }
+      }
+    },
+    {
+      "code": "STK3004",
+      "severity": "error",
+      "range": {
+        "start": { "byteOffset": 108, "line": 6, "column": 19 },
+        "end": { "byteOffset": 113, "line": 6, "column": 24 }
+      }
+    }
+  ]
+}
diff --git a/conformance/invalid/independent-semantic-errors/source.stack b/conformance/invalid/independent-semantic-errors/source.stack
new file mode 100644
index 0000000..9a8f424
--- /dev/null
+++ b/conformance/invalid/independent-semantic-errors/source.stack
@@ -0,0 +1,7 @@
+stack 2.0
+diagram " Bad " {
+  group empty "Empty" {}
+  node Bad ""
+  node Bad "Duplicate"
+  edge missing -> empty
+}
diff --git a/conformance/invalid/invalid-string-escape/expected.diagnostics.json b/conformance/invalid/invalid-string-escape/expected.diagnostics.json
new file mode 100644
index 0000000..1afc9c7
--- /dev/null
+++ b/conformance/invalid/invalid-string-escape/expected.diagnostics.json
@@ -0,0 +1,13 @@
+{
+  "schemaVersion": "1.0",
+  "diagnostics": [
+    {
+      "code": "STK1003",
+      "severity": "error",
+      "range": {
+        "start": { "byteOffset": 23, "line": 2, "column": 14 },
+        "end": { "byteOffset": 23, "line": 2, "column": 14 }
+      }
+    }
+  ]
+}
diff --git a/conformance/invalid/invalid-string-escape/source.stack b/conformance/invalid/invalid-string-escape/source.stack
new file mode 100644
index 0000000..1ffa5a9
--- /dev/null
+++ b/conformance/invalid/invalid-string-escape/source.stack
@@ -0,0 +1,4 @@
+stack 1.0
+diagram "Bad\q" {
+  node api "API"
+}
diff --git a/conformance/invalid/invalid-utf8/expected.diagnostics.json b/conformance/invalid/invalid-utf8/expected.diagnostics.json
new file mode 100644
index 0000000..1ff684c
--- /dev/null
+++ b/conformance/invalid/invalid-utf8/expected.diagnostics.json
@@ -0,0 +1,13 @@
+{
+  "schemaVersion": "1.0",
+  "diagnostics": [
+    {
+      "code": "STK1001",
+      "severity": "error",
+      "range": {
+        "start": { "byteOffset": 17, "line": 2, "column": 5 },
+        "end": { "byteOffset": 17, "line": 2, "column": 5 }
+      }
+    }
+  ]
+}
diff --git a/conformance/invalid/invalid-utf8/source.stack b/conformance/invalid/invalid-utf8/source.stack
new file mode 100644
index 0000000..9597601
--- /dev/null
+++ b/conformance/invalid/invalid-utf8/source.stack
@@ -0,0 +1,2 @@
+stack 1.0
+// 図ÿ
\ No newline at end of file
diff --git a/conformance/invalid/layout-rules/expected.diagnostics.json b/conformance/invalid/layout-rules/expected.diagnostics.json
new file mode 100644
index 0000000..6954c16
--- /dev/null
+++ b/conformance/invalid/layout-rules/expected.diagnostics.json
@@ -0,0 +1,37 @@
+{
+  "schemaVersion": "1.0",
+  "diagnostics": [
+    {
+      "code": "STK3012",
+      "severity": "error",
+      "range": {
+        "start": { "byteOffset": 100, "line": 7, "column": 15 },
+        "end": { "byteOffset": 104, "line": 7, "column": 19 }
+      }
+    },
+    {
+      "code": "STK3011",
+      "severity": "error",
+      "range": {
+        "start": { "byteOffset": 123, "line": 8, "column": 19 },
+        "end": { "byteOffset": 130, "line": 8, "column": 26 }
+      }
+    },
+    {
+      "code": "STK3011",
+      "severity": "error",
+      "range": {
+        "start": { "byteOffset": 146, "line": 9, "column": 15 },
+        "end": { "byteOffset": 147, "line": 9, "column": 16 }
+      }
+    },
+    {
+      "code": "STK3012",
+      "severity": "error",
+      "range": {
+        "start": { "byteOffset": 155, "line": 11, "column": 3 },
+        "end": { "byteOffset": 181, "line": 11, "column": 29 }
+      }
+    }
+  ]
+}
diff --git a/conformance/invalid/layout-rules/source.stack b/conformance/invalid/layout-rules/source.stack
new file mode 100644
index 0000000..f986a6d
--- /dev/null
+++ b/conformance/invalid/layout-rules/source.stack
@@ -0,0 +1,12 @@
+stack 1.0
+diagram "Layout" {
+  node a "A"
+  node b "B"
+  layout {
+    direction right
+    direction down
+    rank same [a, missing]
+    order [a, a]
+  }
+  layout { direction right }
+}
diff --git a/conformance/invalid/nested-group-icon/expected.diagnostics.json b/conformance/invalid/nested-group-icon/expected.diagnostics.json
new file mode 100644
index 0000000..274b9a4
--- /dev/null
+++ b/conformance/invalid/nested-group-icon/expected.diagnostics.json
@@ -0,0 +1,21 @@
+{
+  "schemaVersion": "1.0",
+  "diagnostics": [
+    {
+      "code": "STK3010",
+      "severity": "error",
+      "range": {
+        "start": { "byteOffset": 113, "line": 6, "column": 15 },
+        "end": { "byteOffset": 117, "line": 6, "column": 19 }
+      }
+    },
+    {
+      "code": "STK3013",
+      "severity": "error",
+      "range": {
+        "start": { "byteOffset": 161, "line": 7, "column": 35 },
+        "end": { "byteOffset": 171, "line": 7, "column": 45 }
+      }
+    }
+  ]
+}
diff --git a/conformance/invalid/nested-group-icon/source.stack b/conformance/invalid/nested-group-icon/source.stack
new file mode 100644
index 0000000..f648814
--- /dev/null
+++ b/conformance/invalid/nested-group-icon/source.stack
@@ -0,0 +1,12 @@
+stack 1.0
+diagram "Nested" {
+  group one "One" {
+    group two "Two" {
+      group three "Three" {
+        group four "Four" {
+          node leaf "Leaf" { icon "Bad_icon" }
+        }
+      }
+    }
+  }
+}
diff --git a/conformance/invalid/unexpected-end/expected.diagnostics.json b/conformance/invalid/unexpected-end/expected.diagnostics.json
new file mode 100644
index 0000000..6f0ca54
--- /dev/null
+++ b/conformance/invalid/unexpected-end/expected.diagnostics.json
@@ -0,0 +1,13 @@
+{
+  "schemaVersion": "1.0",
+  "diagnostics": [
+    {
+      "code": "STK2003",
+      "severity": "error",
+      "range": {
+        "start": { "byteOffset": 50, "line": 4, "column": 1 },
+        "end": { "byteOffset": 50, "line": 4, "column": 1 }
+      }
+    }
+  ]
+}
diff --git a/conformance/invalid/unexpected-end/source.stack b/conformance/invalid/unexpected-end/source.stack
new file mode 100644
index 0000000..b42ec4e
--- /dev/null
+++ b/conformance/invalid/unexpected-end/source.stack
@@ -0,0 +1,3 @@
+stack 1.0
+diagram "Incomplete" {
+  node api "API"
diff --git a/conformance/invalid/unexpected-token/expected.diagnostics.json b/conformance/invalid/unexpected-token/expected.diagnostics.json
new file mode 100644
index 0000000..bcd0bec
--- /dev/null
+++ b/conformance/invalid/unexpected-token/expected.diagnostics.json
@@ -0,0 +1,13 @@
+{
+  "schemaVersion": "1.0",
+  "diagnostics": [
+    {
+      "code": "STK2002",
+      "severity": "error",
+      "range": {
+        "start": { "byteOffset": 35, "line": 3, "column": 3 },
+        "end": { "byteOffset": 41, "line": 3, "column": 9 }
+      }
+    }
+  ]
+}
diff --git a/conformance/invalid/unexpected-token/source.stack b/conformance/invalid/unexpected-token/source.stack
new file mode 100644
index 0000000..3b98620
--- /dev/null
+++ b/conformance/invalid/unexpected-token/source.stack
@@ -0,0 +1,4 @@
+stack 1.0
+diagram "Unexpected" {
+  server api "API"
+}
diff --git a/scripts/validate-compiler-diagnostics.py b/scripts/validate-compiler-diagnostics.py
new file mode 100644
index 0000000..b57dd84
--- /dev/null
+++ b/scripts/validate-compiler-diagnostics.py
@@ -0,0 +1,58 @@
+import json
+from pathlib import Path
+
+
+REQUIRED_COMPILER_DIAGNOSTICS = {
+    "STK1001",
+    "STK1002",
+    "STK1003",
+    "STK2001",
+    "STK2002",
+    "STK2003",
+    "STK3001",
+    "STK3002",
+    "STK3003",
+    "STK3004",
+    "STK3005",
+    "STK3006",
+    "STK3007",
+    "STK3008",
+    "STK3009",
+    "STK3010",
+    "STK3011",
+    "STK3012",
+    "STK3013",
+    "STK3014",
+    "STK4002",
+    "STK4003",
+}
+
+
+def main() -> None:
+    root = Path(__file__).resolve().parent.parent
+    observed = set()
+    for path in sorted((root / "conformance").glob("*/*/expected.diagnostics.json")):
+        document = json.loads(path.read_bytes())
+        observed.update(diagnostic["code"] for diagnostic in document["diagnostics"])
+
+    missing = sorted(REQUIRED_COMPILER_DIAGNOSTICS - observed)
+    if missing:
+        raise SystemExit(f"missing compiler diagnostic expectations: {', '.join(missing)}")
+
+    invalid_utf8 = (root / "conformance/invalid/invalid-utf8/source.stack").read_bytes()
+    try:
+        invalid_utf8.decode("utf-8")
+    except UnicodeDecodeError:
+        pass
+    else:
+        raise SystemExit("invalid-utf8/source.stack must contain invalid UTF-8")
+    if b"\r\n" not in invalid_utf8:
+        raise SystemExit("invalid-utf8/source.stack must exercise CRLF positions")
+
+    byte_order_mark = (root / "conformance/invalid/byte-order-mark/source.stack").read_bytes()
+    if not byte_order_mark.startswith(b"\xef\xbb\xbf"):
+        raise SystemExit("byte-order-mark/source.stack must begin with a UTF-8 BOM")
+
+
+if __name__ == "__main__":
+    main()