fix(prompts): fix three infrastructure bugs in prompt dependency resolution

- ContentMacro: add __post_init__ to auto-derive raw_text when built
  programmatically, preventing str.replace("", X) corruption
- MacroParser: add @{target} shorthand syntax support mapped to REQUIRED kind,
  updating parse, has_macros, count_macros, and find_macro_positions
- Artifact: store content in model and SQLite DB, replace resolver placeholder
  with actual artifact content, add migration for existing databases

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/unit/prompts/test_context_compiler.py

@@ -97,7 +97,7 @@ class TestContextCompiler:
 
         # Macro should be replaced with resolved content
         assert "{{require:intro}}" not in compiled.content
-        assert "[Content of intro from space-1]" in compiled.content
+        assert "Introduction text" in compiled.content
         assert "intro" in compiled.dependency_digests
 
     def test_compile_with_optional_macros_substitutes_empty(
@@ -126,7 +126,7 @@ class TestContextCompiler:
 
         # Optional missing macro should be removed
         assert "{{optional:missing}}" not in compiled.content
-        assert compiled.content == "Start [Content of present from space-1] middle  end"
+        assert compiled.content == "Start Present content middle  end"
 
     def test_compile_failed_resolution_raises_error(
         self, compiler, analyzer, resolver
@@ -257,3 +257,32 @@ class TestContextCompiler:
         assert info["dependency_count"] == 1
         assert "dep" in info["dependencies"]
         assert info["is_partial"] is False
+
+    def test_compile_with_programmatic_macros_no_corruption(
+        self, compiler, analyzer, resolver, artifact_service
+    ):
+        """Test that compilation with programmatic macros doesn't corrupt content."""
+        artifact_service.create_artifact(
+            space_id="space-1",
+            name="dep",
+            content="Dependency content",
+        )
+
+        # Use @{target} shorthand syntax (parsed into programmatic macros)
+        content = "Before @{dep} after"
+        template = PromptTemplate.create(
+            space_id="space-1",
+            name="test",
+            content=content,
+        )
+        analyzer.analyze(template, content)
+
+        config = ResolutionConfig(space_id="space-1")
+        result = resolver.resolve_template(template, config)
+
+        compiled = compiler.compile(template, content, result)
+
+        # Content should be cleanly substituted, not corrupted
+        assert "@{dep}" not in compiled.content
+        assert "Dependency content" in compiled.content
+        assert compiled.content == "Before Dependency content after"