Implement HC014: Missing Entrypoint detection

## Overview
Detects when no valid entrypoint (Main.main or main) exists in analyzed code.

## Implementation Details
- **Rule**: `rule_missing_entrypoint.hako` following single-responsibility box principles
- **Detection**: Checks if any entrypoint from entrypoints[] exists in methods[]
- **Pattern Matching**: Matches "Main.main" or "main" with any arity (e.g., Main.main/0, Main.main/1)
- **Integration**: Added to cli.hako with debug output support

## Test Cases
- **ok.hako**: Main box with main() method → no warning
- **ng.hako**: Main box with run() method (not main) → HC014 + HC011 warnings
  - HC011: Main.run/0 unreachable (no entrypoint calling it)
  - HC014: Missing entrypoint (correct cascading diagnostics)

## Test Results
```
[TEST/OK] HC011_dead_methods
[TEST/OK] HC012_dead_static_box
[TEST/OK] HC013_duplicate_method
[TEST/OK] HC014_missing_entrypoint ← NEW
[TEST/OK] HC016_unused_alias
[TEST/SUMMARY] all green
```

## Architecture
- Box-first design: RuleMissingEntrypointBox with single responsibility
- Helper method: _has_entrypoint_method() for clean separation of concerns
- Diagnostic format: "[HC014] missing entrypoint (Main.main or main)"
- Severity: "warning" (non-blocking, informational)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

tools/hako_check/cli.hako

@@ -11,6 +11,7 @@ using tools.hako_check.rules.rule_unused_alias as RuleUnusedAliasBox
 using tools.hako_check.rules.rule_non_ascii_quotes as RuleNonAsciiQuotesBox
 using tools.hako_check.rules.rule_dead_static_box as RuleDeadStaticBoxBox
 using tools.hako_check.rules.rule_duplicate_method as RuleDuplicateMethodBox
+using tools.hako_check.rules.rule_missing_entrypoint as RuleMissingEntrypointBox
 using tools.hako_check.render.graphviz as GraphvizRenderBox
 using tools.hako_parser.parser_core as HakoParserCoreBox
 
@@ -101,6 +102,13 @@ static box HakoAnalyzerBox {
         local added = after_n - before_n
         print("[hako_check/HC013] file=" + p + " added=" + me._itoa(added) + " total_out=" + me._itoa(after_n))
       }
+      before_n = out.size()
+      RuleMissingEntrypointBox.apply_ir(ir, p, out)
+      if debug == 1 {
+        local after_n = out.size()
+        local added = after_n - before_n
+        print("[hako_check/HC014] file=" + p + " added=" + me._itoa(added) + " total_out=" + me._itoa(after_n))
+      }
       // suppression: HC012(dead box) > HC011(unreachable method)
       local filtered = me._suppress_overlap(out)
       // flush (text only)

tools/hako_check/rules/rule_missing_entrypoint.hako

@@ -0,0 +1,64 @@
+// tools/hako_check/rules/rule_missing_entrypoint.hako — HC014: Missing Entrypoint
+// Detect when no entrypoint (Main.main or main) exists in the analyzed code.
+
+using selfhost.shared.common.string_helpers as Str
+
+static box RuleMissingEntrypointBox {
+  method apply_ir(ir, path, out) {
+    local entrypoints = ir.get("entrypoints")
+    if entrypoints == null { return 0 }
+
+    local methods = ir.get("methods")
+    if methods == null || methods.size() == 0 {
+      // No methods at all - definitely missing entrypoint
+      out.push("[HC014] missing entrypoint (Main.main or main)")
+      return out.size()
+    }
+
+    // Check if any entrypoint exists
+    local found = 0
+    local ei = 0
+    while ei < entrypoints.size() {
+      local ep = entrypoints.get(ei)
+      if me._has_entrypoint_method(methods, ep) == 1 {
+        found = 1
+        break
+      }
+      ei = ei + 1
+    }
+
+    // If no entrypoint found, report error
+    if found == 0 {
+      out.push("[HC014] missing entrypoint (Main.main or main)")
+    }
+
+    return out.size()
+  }
+
+  _has_entrypoint_method(methods, ep_name) {
+    // Check if method starting with ep_name exists
+    // e.g., "Main.main" matches "Main.main/0", "Main.main/1", etc.
+    // "main" matches "main/0", etc.
+    local mi = 0
+    while mi < methods.size() {
+      local m = methods.get(mi)
+      if m == null { mi = mi + 1; continue }
+
+      // Check exact match with arity suffix
+      // ep_name can be "Main.main" or "main"
+      local len = ep_name.length()
+      if m.length() >= len + 2 {
+        local prefix = m.substring(0, len)
+        if prefix == ep_name {
+          // Check if followed by "/" (arity separator)
+          local next_char = m.substring(len, len+1)
+          if next_char == "/" { return 1 }
+        }
+      }
+      mi = mi + 1
+    }
+    return 0
+  }
+}
+
+static box RuleMissingEntrypointMain { method main(args) { return 0 } }

tools/hako_check/tests/HC014_missing_entrypoint/expected.json

@@ -0,0 +1,4 @@
+{"diagnostics":[
+  {"file":"ng.hako","line":1,"rule":"HC011","message":"[HC011] unreachable method (dead code): PLACEHOLDER :: Main.run/0","quickFix":"Remove or reference the dead method from an entrypoint","severity":"error"},
+  {"file":"ng.hako","line":1,"rule":"HC014","message":"[HC014] missing entrypoint (Main.main or main)","quickFix":"","severity":"warning"}
+]}

tools/hako_check/tests/HC014_missing_entrypoint/ng.hako

@@ -0,0 +1,7 @@
+// ng.hako — missing Main.main entrypoint
+
+static box Main {
+  method run() {
+    return 0
+  }
+}

tools/hako_check/tests/HC014_missing_entrypoint/ok.hako

@@ -0,0 +1,14 @@
+// ok.hako — has Main.main entrypoint
+
+static box Helper {
+  method calculate(x) {
+    return x * 2
+  }
+}
+
+static box Main {
+  method main() {
+    Helper.calculate(42)
+    return 0
+  }
+}