diff --git a/conformance/native/fail/char-hex-7f.0 b/conformance/native/fail/char-hex-7f.0
new file mode 100644
index 000000000..f8068c119
--- /dev/null
+++ b/conformance/native/fail/char-hex-7f.0
@@ -0,0 +1,4 @@
+pub fn main(world: World) -> Void raises {
+    let bad: char = '\x80'
+    check world.out.write("boundary hex\n")
+}
diff --git a/conformance/native/fail/char-hex-high.0 b/conformance/native/fail/char-hex-high.0
new file mode 100644
index 000000000..927756d96
--- /dev/null
+++ b/conformance/native/fail/char-hex-high.0
@@ -0,0 +1,4 @@
+pub fn main(world: World) -> Void raises {
+    let bad: char = '\xFF'
+    check world.out.write("high hex\n")
+}
diff --git a/conformance/native/fail/malformed-float-underscores.0 b/conformance/native/fail/malformed-float-underscores.0
new file mode 100644
index 000000000..e123405a8
--- /dev/null
+++ b/conformance/native/fail/malformed-float-underscores.0
@@ -0,0 +1,4 @@
+pub fn main(world: World) -> Void raises {
+    let bad: f64 = 1.0_
+    check world.out.write("malformed underscore float\n")
+}
diff --git a/conformance/native/fail/string-null-escape.0 b/conformance/native/fail/string-null-escape.0
new file mode 100644
index 000000000..39ef035e8
--- /dev/null
+++ b/conformance/native/fail/string-null-escape.0
@@ -0,0 +1,4 @@
+pub fn main(world: World) -> Void raises {
+    let bad: String = "\0"
+    check world.out.write("null escape\n")
+}
diff --git a/conformance/native/fail/string-unknown-escape.0 b/conformance/native/fail/string-unknown-escape.0
new file mode 100644
index 000000000..dc7938678
--- /dev/null
+++ b/conformance/native/fail/string-unknown-escape.0
@@ -0,0 +1,4 @@
+pub fn main(world: World) -> Void raises {
+    let bad: String = "\q"
+    check world.out.write("unknown escape\n")
+}
diff --git a/conformance/native/pass/float-literal-underscores.0 b/conformance/native/pass/float-literal-underscores.0
new file mode 100644
index 000000000..c84679d9c
--- /dev/null
+++ b/conformance/native/pass/float-literal-underscores.0
@@ -0,0 +1,9 @@
+pub fn main(world: World) -> Void raises {
+    let grouped: f64 = 1_000.5
+    let tiny: f64 = 0.0_5
+    let exponent: f64 = 1.0e1_0
+    let default_width: f64 = 1_000.0
+    if grouped == 1000.5 && tiny == 0.05 && exponent == 1.0e10 && default_width == 1000.0 {
+        check world.out.write("float literal underscores ok\n")
+    }
+}
diff --git a/conformance/native/pass/string-escape-canonical.0 b/conformance/native/pass/string-escape-canonical.0
new file mode 100644
index 000000000..22445840b
--- /dev/null
+++ b/conformance/native/pass/string-escape-canonical.0
@@ -0,0 +1,22 @@
+pub fn main(world: World) -> Void raises {
+    let newline: String = "a\nb"
+    if std.mem.eqlBytes(std.mem.span(newline), std.mem.span("a\nb")) {
+        check world.out.write("newline ok\n")
+    }
+    let tab: String = "x\ty"
+    if std.mem.eqlBytes(std.mem.span(tab), std.mem.span("x\ty")) {
+        check world.out.write("tab ok\n")
+    }
+    let quote: String = "say \"hi\""
+    if std.mem.eqlBytes(std.mem.span(quote), std.mem.span("say \"hi\"")) {
+        check world.out.write("quote ok\n")
+    }
+    let backslash: String = "path\\to\\file"
+    if std.mem.eqlBytes(std.mem.span(backslash), std.mem.span("path\\to\\file")) {
+        check world.out.write("backslash ok\n")
+    }
+    let hex: String = "byte \x41 here"
+    if std.mem.eqlBytes(std.mem.span(hex), std.mem.span("byte \x41 here")) {
+        check world.out.write("hex ok\n")
+    }
+}
diff --git a/conformance/run.mjs b/conformance/run.mjs
index e619dc7bc..ba240dbce 100644
--- a/conformance/run.mjs
+++ b/conformance/run.mjs
@@ -459,6 +459,7 @@ for (const fixture of [
   "conformance/native/pass/explicit-casts.0",
   "conformance/native/pass/float-char-casts.0",
   "conformance/native/pass/radix-suffix-literals.0",
+  "conformance/native/pass/float-literal-underscores.0",
   "conformance/native/pass/char-literals.0",
   "conformance/native/pass/float-primitives.0",
   "conformance/native/pass/wrapping-saturating-arithmetic.0",
@@ -490,6 +491,7 @@ for (const fixture of [
   "conformance/native/pass/byte-view-call-single-eval.0",
   "conformance/native/pass/generic-spans.0",
   "conformance/native/pass/open-ended-slices.0",
+  "conformance/native/pass/string-escape-canonical.0",
   "conformance/native/pass/string-slices.0",
   "conformance/native/pass/string-param-span-slice.0",
   "conformance/native/pass/coff-dynamic-byte-slice.0",
@@ -916,6 +918,7 @@ assert.equal(agentSurfaceOwnedDropReadinessBody.targetReadiness.ok, false);
 assert.equal(agentSurfaceOwnedDropReadinessBody.targetReadiness.buildable, false);
 assert.equal(agentSurfaceOwnedDropReadinessBody.targetReadiness.languageOk, true);
 assert.equal(agentSurfaceOwnedDropReadinessBody.targetReadiness.diagnostics[0].code, "BLD004");
+assert.match(agentSurfaceOwnedDropReadinessBody.targetReadiness.diagnostics[0].message, /direct ELF64 local type is unsupported/);
 assert.deepEqual(agentSurfaceOwnedDropReadinessBody.targetReadiness.diagnostics[0].backendBlocker, {
   target: "linux-musl-x64",
   objectFormat: "elf",
@@ -924,6 +927,32 @@ assert.deepEqual(agentSurfaceOwnedDropReadinessBody.targetReadiness.diagnostics[
   unsupportedFeature: "owned<Tracked>",
 });
 
+const agentSurfaceOwnedDropCoffReadiness = await execFileAsync(zero, [
+  "check",
+  "--json",
+  "--emit",
+  "obj",
+  "--target",
+  "win32-x64.exe",
+  "conformance/agent-surface/fixtures/owned-drop-direct-backend-unsupported.0",
+]);
+const agentSurfaceOwnedDropCoffReadinessBody = JSON.parse(agentSurfaceOwnedDropCoffReadiness.stdout);
+assert.equal(agentSurfaceOwnedDropCoffReadinessBody.targetReadiness.diagnostics[0].code, "BLD004");
+assert.match(agentSurfaceOwnedDropCoffReadinessBody.targetReadiness.diagnostics[0].message, /direct COFF x64 local type is unsupported/);
+
+const agentSurfaceOwnedDropMachoReadiness = await execFileAsync(zero, [
+  "check",
+  "--json",
+  "--emit",
+  "obj",
+  "--target",
+  "darwin-x64",
+  "conformance/agent-surface/fixtures/owned-drop-direct-backend-unsupported.0",
+]);
+const agentSurfaceOwnedDropMachoReadinessBody = JSON.parse(agentSurfaceOwnedDropMachoReadiness.stdout);
+assert.equal(agentSurfaceOwnedDropMachoReadinessBody.targetReadiness.diagnostics[0].code, "BLD004");
+assert.match(agentSurfaceOwnedDropMachoReadinessBody.targetReadiness.diagnostics[0].message, /direct x86_64 Mach-O local type is unsupported/);
+
 const directCallExeReadiness = await execFileAsync(zero, [
   "check",
   "--json",
@@ -5025,6 +5054,22 @@ const charBadEscape = await execFileAsync(zero, ["check", "conformance/native/fa
 assert.notEqual(charBadEscape.code, 0);
 assert.match(charBadEscape.stderr, /PAR100/);
 
+const charHexHigh = await execFileAsync(zero, ["check", "conformance/native/fail/char-hex-high.0"]).catch((error) => error);
+assert.notEqual(charHexHigh.code, 0);
+assert.match(charHexHigh.stderr, /PAR100/);
+
+const charHex7f = await execFileAsync(zero, ["check", "conformance/native/fail/char-hex-7f.0"]).catch((error) => error);
+assert.notEqual(charHex7f.code, 0);
+assert.match(charHex7f.stderr, /PAR100/);
+
+const stringUnknownEscape = await execFileAsync(zero, ["check", "conformance/native/fail/string-unknown-escape.0"]).catch((error) => error);
+assert.notEqual(stringUnknownEscape.code, 0);
+assert.match(stringUnknownEscape.stderr, /PAR100/);
+
+const stringNullEscape = await execFileAsync(zero, ["check", "conformance/native/fail/string-null-escape.0"]).catch((error) => error);
+assert.notEqual(stringNullEscape.code, 0);
+assert.match(stringNullEscape.stderr, /PAR100/);
+
 const charToString = await execFileAsync(zero, ["check", "conformance/native/fail/char-to-string.0"]).catch((error) => error);
 assert.notEqual(charToString.code, 0);
 assert.match(charToString.stderr, /TYP002/);
@@ -5041,6 +5086,10 @@ const malformedFloatLiteral = await execFileAsync(zero, ["check", "conformance/n
 assert.notEqual(malformedFloatLiteral.code, 0);
 assert.match(malformedFloatLiteral.stderr, /TYP019/);
 
+const malformedFloatUnderscores = await execFileAsync(zero, ["check", "conformance/native/fail/malformed-float-underscores.0"]).catch((error) => error);
+assert.notEqual(malformedFloatUnderscores.code, 0);
+assert.match(malformedFloatUnderscores.stderr, /TYP019/);
+
 const floatF32Overflow = await execFileAsync(zero, ["check", "conformance/native/fail/float-f32-overflow.0"]).catch((error) => error);
 assert.notEqual(floatF32Overflow.code, 0);
 assert.match(floatF32Overflow.stderr, /TYP020/);
diff --git a/native/zero-c/include/zero.h b/native/zero-c/include/zero.h
index 8895dbe2d..776d324c5 100644
--- a/native/zero-c/include/zero.h
+++ b/native/zero-c/include/zero.h
@@ -973,6 +973,7 @@ ZDirectRuntimeObjectFacts z_direct_runtime_object_facts(const ZTargetInfo *targe
 ZDirectExecutableTargetFacts z_direct_executable_target_facts(const ZTargetInfo *target, const char *requested_backend);
 const char *z_direct_backend_expected(const ZTargetInfo *target);
 const char *z_direct_backend_help(const ZTargetInfo *target);
+const char *z_direct_backend_target_label(const ZTargetInfo *target);
 void z_append_http_runtime_json(ZBuf *buf, const ZTargetInfo *target);
 void z_append_targets_json(ZBuf *buf);
 void z_append_target_names_json(ZBuf *buf);
diff --git a/native/zero-c/src/buildability_context.c b/native/zero-c/src/buildability_context.c
index e379def94..2ec8306dd 100644
--- a/native/zero-c/src/buildability_context.c
+++ b/native/zero-c/src/buildability_context.c
@@ -121,7 +121,12 @@ bool z_build_diag(const ZBuildability *ctx, ZDiag *diag, const char *message, in
   diag->line = line > 0 ? line : 1;
   diag->column = column > 0 ? column : 1;
   diag->length = 1;
-  snprintf(diag->message, sizeof(diag->message), "%s", message ? message : "direct backend buildability check failed");
+  const char *label = ctx ? z_direct_backend_target_label(ctx->target) : NULL;
+  if (label && message && strncmp(message, "direct backend ", 15) == 0) {
+    snprintf(diag->message, sizeof(diag->message), "direct %s %s", label, message + 15);
+  } else {
+    snprintf(diag->message, sizeof(diag->message), "%s", message ? message : "direct backend buildability check failed");
+  }
   snprintf(diag->expected, sizeof(diag->expected), "%s", ctx && ctx->expected ? ctx->expected : "direct backend buildability subset");
   snprintf(diag->actual, sizeof(diag->actual), "%s", actual && actual[0] ? actual : "unsupported construct");
   snprintf(diag->help, sizeof(diag->help), "%s", ctx && ctx->help ? ctx->help : "choose a supported direct target or simplify the program for this backend");
diff --git a/native/zero-c/src/canonical_text.c b/native/zero-c/src/canonical_text.c
index 1bc0a62f7..83b6fbe44 100644
--- a/native/zero-c/src/canonical_text.c
+++ b/native/zero-c/src/canonical_text.c
@@ -211,9 +211,14 @@ static bool canon_scan_char(const char *source, size_t *offset, int *column, ZCa
     if (escaped == 'x') {
       char high_ch = source[*offset + 1];
       char low_ch = high_ch ? source[*offset + 2] : 0;
-      if (canon_hex_digit(high_ch) < 0 || canon_hex_digit(low_ch) < 0) {
+      int high = canon_hex_digit(high_ch);
+      int low = canon_hex_digit(low_ch);
+      if (high < 0 || low < 0) {
         return canon_fail(diag, &at_start, "malformed hex character escape", "two hex digits", "invalid escape");
       }
+      if (((high << 4) | low) >= 0x80) {
+        return canon_fail(diag, &at_start, "character literal must be one byte", "ASCII byte", "non-ASCII");
+      }
       *offset += 3;
       *column += 3;
     } else {
diff --git a/native/zero-c/src/canonical_text_program.c b/native/zero-c/src/canonical_text_program.c
index 7c903f870..a3ad39d7b 100644
--- a/native/zero-c/src/canonical_text_program.c
+++ b/native/zero-c/src/canonical_text_program.c
@@ -148,8 +148,12 @@ static char *canon_ast_decode_string_literal(const ZCanonicalToken *token, ZDiag
       }
       zbuf_append_char(&buf, (char)value);
       i += 2;
-    } else {
+    } else if (escaped == '\\' || escaped == '\'' || escaped == '"') {
       zbuf_append_char(&buf, escaped);
+    } else {
+      canon_ast_fail(diag, token, "invalid string escape", "escaped byte", text);
+      free(buf.data);
+      return z_strdup("");
     }
   }
   if (canon_ast_has_diag(diag)) {
diff --git a/native/zero-c/src/checker.c b/native/zero-c/src/checker.c
index 88a0be471..b1dd6303e 100644
--- a/native/zero-c/src/checker.c
+++ b/native/zero-c/src/checker.c
@@ -5501,25 +5501,42 @@ static bool validate_integer_literal_for_type(const Expr *expr, const char *expe
 
 static bool parse_float_literal(const char *text, double *out, bool *out_of_range) {
   if (!text || !text[0]) return false;
-  if (strchr(text, '_')) return false;
+  char stripped[64];
+  size_t write = 0;
+  bool previous_underscore = false;
+  bool saw_any_digit = false;
+  for (size_t read = 0; text[read] != 0 && write + 1 < sizeof(stripped); read++) {
+    char ch = text[read];
+    if (ch == '_') {
+      if (!saw_any_digit || previous_underscore) return false;
+      previous_underscore = true;
+      continue;
+    }
+    stripped[write++] = ch;
+    previous_underscore = false;
+    if (ch >= '0' && ch <= '9') saw_any_digit = true;
+  }
+  if (previous_underscore || !saw_any_digit || write == 0 || write + 1 >= sizeof(stripped)) return false;
+  stripped[write] = 0;
+
   size_t index = 0;
-  if (!isdigit((unsigned char)text[index])) return false;
-  while (isdigit((unsigned char)text[index])) index++;
-  if (text[index] != '.') return false;
+  if (!isdigit((unsigned char)stripped[index])) return false;
+  while (isdigit((unsigned char)stripped[index])) index++;
+  if (stripped[index] != '.') return false;
   index++;
-  if (!isdigit((unsigned char)text[index])) return false;
-  while (isdigit((unsigned char)text[index])) index++;
-  if (text[index] == 'e' || text[index] == 'E') {
+  if (!isdigit((unsigned char)stripped[index])) return false;
+  while (isdigit((unsigned char)stripped[index])) index++;
+  if (stripped[index] == 'e' || stripped[index] == 'E') {
     index++;
-    if (text[index] == '+' || text[index] == '-') index++;
-    if (!isdigit((unsigned char)text[index])) return false;
-    while (isdigit((unsigned char)text[index])) index++;
+    if (stripped[index] == '+' || stripped[index] == '-') index++;
+    if (!isdigit((unsigned char)stripped[index])) return false;
+    while (isdigit((unsigned char)stripped[index])) index++;
   }
-  if (text[index] != 0) return false;
+  if (stripped[index] != 0) return false;
 
   errno = 0;
   char *end = NULL;
-  double value = strtod(text, &end);
+  double value = strtod(stripped, &end);
   if (!end || *end != 0) return false;
   *out = value;
   *out_of_range = errno == ERANGE;
diff --git a/native/zero-c/src/main.c b/native/zero-c/src/main.c
index 5d94dfb7d..8338cf2da 100644
--- a/native/zero-c/src/main.c
+++ b/native/zero-c/src/main.c
@@ -9911,9 +9911,17 @@ static void init_lowering_backend_diag(ZDiag *diag, const SourceInput *input, co
   diag->line = ir && ir->mir_line > 0 ? ir->mir_line : 1;
   diag->column = ir && ir->mir_column > 0 ? ir->mir_column : 1;
   diag->length = 1;
-  snprintf(diag->message, sizeof(diag->message), "%s",
-           llvm_request ? "LLVM IR backend cannot lower this MIR program yet" :
-           (ir && ir->mir_message[0] ? ir->mir_message : "direct backend lowering failed"));
+  const char *ir_message = ir && ir->mir_message[0] ? ir->mir_message : "direct backend lowering failed";
+  if (llvm_request) {
+    snprintf(diag->message, sizeof(diag->message), "%s", "LLVM IR backend cannot lower this MIR program yet");
+  } else {
+    const char *label = z_direct_backend_target_label(target);
+    if (label && strncmp(ir_message, "direct backend ", 15) == 0) {
+      snprintf(diag->message, sizeof(diag->message), "direct %s %s", label, ir_message + 15);
+    } else {
+      snprintf(diag->message, sizeof(diag->message), "%s", ir_message);
+    }
+  }
   snprintf(diag->expected, sizeof(diag->expected), "%s",
            llvm_request ? "LLVM IR scalar, fixed-array, and byte-view MIR subset" : z_direct_backend_expected(target));
   snprintf(diag->actual, sizeof(diag->actual), "%s", ir && ir->mir_actual[0] ? ir->mir_actual : "unsupported construct");
diff --git a/native/zero-c/src/target_backend.c b/native/zero-c/src/target_backend.c
index c7218deaf..bd54fd321 100644
--- a/native/zero-c/src/target_backend.c
+++ b/native/zero-c/src/target_backend.c
@@ -367,3 +367,16 @@ const char *z_direct_backend_help(const ZTargetInfo *target) {
   if (backend == Z_DIRECT_BACKEND_COFF_X64 || strcmp(format, "coff") == 0) return "reduce the program to primitive direct-backend constructs or choose a supported direct target";
   return "choose a supported direct target or restrict this program to exported primitive integer arithmetic functions";
 }
+
+const char *z_direct_backend_target_label(const ZTargetInfo *target) {
+  ZDirectBackend backend = target ? z_direct_object_backend(target) : Z_DIRECT_BACKEND_NONE;
+  switch (backend) {
+    case Z_DIRECT_BACKEND_ELF64: return "ELF64";
+    case Z_DIRECT_BACKEND_ELF_AARCH64: return "AArch64 ELF";
+    case Z_DIRECT_BACKEND_MACHO64: return "AArch64 Mach-O";
+    case Z_DIRECT_BACKEND_MACHO_X64: return "x86_64 Mach-O";
+    case Z_DIRECT_BACKEND_COFF_X64: return "COFF x64";
+    case Z_DIRECT_BACKEND_COFF_AARCH64: return "COFF AArch64";
+    default: return NULL;
+  }
+}
diff --git a/scripts/compiler-metrics.mts b/scripts/compiler-metrics.mts
index d48e4d641..fef3a32b5 100644
--- a/scripts/compiler-metrics.mts
+++ b/scripts/compiler-metrics.mts
@@ -17,8 +17,8 @@ type CScanState = {
 const fileBudgets = {
   "native/zero-c/include/zero.h": { maxLines: 990, maxStrcmpCalls: 0 },
   "native/zero-c/include/zero_runtime.h": { maxLines: 100, maxStrcmpCalls: 0 },
-  "native/zero-c/src/checker.c": { maxLines: 11710, maxStrcmpCalls: 287 },
-  "native/zero-c/src/main.c": { maxLines: 12975, maxStrcmpCalls: 473 },
+  "native/zero-c/src/checker.c": { maxLines: 11725, maxStrcmpCalls: 287 },
+  "native/zero-c/src/main.c": { maxLines: 12983, maxStrcmpCalls: 473 },
   "native/zero-c/src/ir.c": { maxLines: 4212, maxStrcmpCalls: 229 },
   "native/zero-c/src/llvm_backend_metadata.c": { maxLines: 80, maxStrcmpCalls: 0 },
   "native/zero-c/src/llvm_toolchain.c": { maxLines: 335, maxStrcmpCalls: 19 },
@@ -27,16 +27,16 @@ const fileBudgets = {
   "native/zero-c/src/buildability.c": { maxLines: 295, maxStrcmpCalls: 2 },
   "native/zero-c/src/buildability.h": { maxLines: 20, maxStrcmpCalls: 0 },
   "native/zero-c/src/buildability_internal.h": { maxLines: 40, maxStrcmpCalls: 0 },
-  "native/zero-c/src/buildability_context.c": { maxLines: 185, maxStrcmpCalls: 1 },
+  "native/zero-c/src/buildability_context.c": { maxLines: 200, maxStrcmpCalls: 1 },
   "native/zero-c/src/buildability_targets.c": { maxLines: 190, maxStrcmpCalls: 0 },
   "native/zero-c/src/buildability_value_targets.c": { maxLines: 371, maxStrcmpCalls: 0 },
   "native/zero-c/src/c_import.c": { maxLines: 750, maxStrcmpCalls: 51 },
   "native/zero-c/src/c_import.h": { maxLines: 40, maxStrcmpCalls: 0 },
   "native/zero-c/src/call_resolve.c": { maxLines: 200, maxStrcmpCalls: 2 },
   "native/zero-c/src/call_resolve.h": { maxLines: 100, maxStrcmpCalls: 0 },
-  "native/zero-c/src/canonical_text.c": { maxLines: 1508, maxStrcmpCalls: 0 },
+  "native/zero-c/src/canonical_text.c": { maxLines: 1520, maxStrcmpCalls: 0 },
   "native/zero-c/src/canonical_text_format.c": { maxLines: 354, maxStrcmpCalls: 0 },
-  "native/zero-c/src/canonical_text_program.c": { maxLines: 1493, maxStrcmpCalls: 0 },
+  "native/zero-c/src/canonical_text_program.c": { maxLines: 1510, maxStrcmpCalls: 0 },
   "native/zero-c/src/canonical_text_write.c": { maxLines: 604, maxStrcmpCalls: 2 },
   "native/zero-c/src/canonical_text.h": { maxLines: 80, maxStrcmpCalls: 0 },
   "native/zero-c/src/coff_format.c": { maxLines: 370, maxStrcmpCalls: 0 },
@@ -116,7 +116,7 @@ const fileBudgets = {
   "native/zero-c/src/std_sig.h": { maxLines: 60, maxStrcmpCalls: 0 },
   "native/zero-c/src/std_source.c": { maxLines: 340, maxStrcmpCalls: 2 },
   "native/zero-c/src/std_source.h": { maxLines: 30, maxStrcmpCalls: 0 },
-  "native/zero-c/src/target_backend.c": { maxLines: 369, maxStrcmpCalls: 32 },
+  "native/zero-c/src/target_backend.c": { maxLines: 390, maxStrcmpCalls: 32 },
   "native/zero-c/src/target.c": { maxLines: 465, maxStrcmpCalls: 15 },
   "native/zero-c/src/type_core.c": { maxLines: 900, maxStrcmpCalls: 8 },
   "native/zero-c/src/type_core.h": { maxLines: 150, maxStrcmpCalls: 0 },