Fix --dev extension agent symlinks (#2554)

* Fix dev extension agent symlinks

* Address dev symlink review feedback

* fix: handle dev symlink relpath failures

* fix: fall back when dev cache writes fail

* test: cover dev symlink fallback without privileges

src/specify_cli/agents.py

@@ -439,6 +439,7 @@ class CommandRegistrar:
         project_root: Path,
         context_note: str = None,
         _resolved_dir: Path = None,
+        link_outputs: bool = False,
     ) -> List[str]:
         """Register commands for a specific agent.
 
@@ -453,6 +454,9 @@ class CommandRegistrar:
                 only — avoids a second ``_resolve_agent_dir`` call and
                 duplicate deprecation warnings when invoked from
                 ``register_commands_for_all_agents``).
+            link_outputs: If True, write rendered output to a source-local
+                dev cache and symlink the agent command file to it. Falls back
+                to a normal file write when symlinks are unavailable.
 
         Returns:
             List of registered command names
@@ -559,7 +563,15 @@ class CommandRegistrar:
             dest_file = commands_dir / f"{output_name}{agent_config['extension']}"
             self._ensure_inside(dest_file, commands_dir)
             dest_file.parent.mkdir(parents=True, exist_ok=True)
-            dest_file.write_text(output, encoding="utf-8")
+            self._write_registered_output(
+                dest_file,
+                output,
+                source_dir,
+                agent_name,
+                output_name,
+                agent_config["extension"],
+                link_outputs,
+            )
 
             if agent_name == "copilot":
                 self.write_copilot_prompt(project_root, cmd_name)
@@ -625,13 +637,56 @@ class CommandRegistrar:
                 )
                 self._ensure_inside(alias_file, commands_dir)
                 alias_file.parent.mkdir(parents=True, exist_ok=True)
-                alias_file.write_text(alias_output, encoding="utf-8")
+                self._write_registered_output(
+                    alias_file,
+                    alias_output,
+                    source_dir,
+                    agent_name,
+                    alias_output_name,
+                    agent_config["extension"],
+                    link_outputs,
+                )
                 if agent_name == "copilot":
                     self.write_copilot_prompt(project_root, alias)
                 registered.append(alias)
 
         return registered
 
+    @staticmethod
+    def _write_registered_output(
+        dest_file: Path,
+        content: str,
+        source_dir: Path,
+        agent_name: str,
+        output_name: str,
+        extension: str,
+        link_outputs: bool,
+    ) -> None:
+        """Write a rendered agent artifact, optionally as a dev-mode symlink."""
+        if not link_outputs:
+            dest_file.write_text(content, encoding="utf-8")
+            return
+
+        rel_output = Path(f"{output_name}{extension}")
+        cache_root = source_dir / ".specify-dev" / "agent-commands" / agent_name
+        cache_file = cache_root / rel_output
+        CommandRegistrar._ensure_inside(cache_file, cache_root)
+
+        try:
+            cache_file.parent.mkdir(parents=True, exist_ok=True)
+            cache_file.write_text(content, encoding="utf-8")
+            if dest_file.exists() or dest_file.is_symlink():
+                dest_file.unlink()
+            target = os.path.relpath(cache_file, dest_file.parent)
+            os.symlink(target, dest_file)
+        except (OSError, ValueError):
+            # Windows often requires Developer Mode or admin privileges for
+            # symlinks, and relpath can fail across drives. Keep dev installs
+            # functional by falling back to a copy.
+            if dest_file.is_symlink():
+                dest_file.unlink()
+            dest_file.write_text(content, encoding="utf-8")
+
     @staticmethod
     def write_copilot_prompt(project_root: Path, cmd_name: str) -> None:
         """Generate a companion .prompt.md file for a Copilot agent command.
@@ -700,6 +755,7 @@ class CommandRegistrar:
         source_dir: Path,
         project_root: Path,
         context_note: str = None,
+        link_outputs: bool = False,
     ) -> Dict[str, List[str]]:
         """Register commands for all detected agents in the project.
 
@@ -709,6 +765,8 @@ class CommandRegistrar:
             source_dir: Directory containing command source files
             project_root: Path to project root
             context_note: Custom context comment for markdown output
+            link_outputs: If True, create dev-mode symlinks for rendered
+                command files when supported by the OS.
 
         Returns:
             Dictionary mapping agent names to list of registered commands
@@ -740,6 +798,7 @@ class CommandRegistrar:
                         project_root,
                         context_note=context_note,
                         _resolved_dir=agent_dir,
+                        link_outputs=link_outputs,
                     )
                     if registered:
                         results[agent_name] = registered
@@ -755,6 +814,7 @@ class CommandRegistrar:
         source_dir: Path,
         project_root: Path,
         context_note: Optional[str] = None,
+        link_outputs: bool = False,
     ) -> Dict[str, List[str]]:
         """Register commands for all non-skill agents in the project.
 
@@ -768,6 +828,8 @@ class CommandRegistrar:
             source_dir: Directory containing command source files
             project_root: Path to project root
             context_note: Custom context comment for markdown output
+            link_outputs: If True, create dev-mode symlinks for rendered
+                command files when supported by the OS.
 
         Returns:
             Dictionary mapping agent names to list of registered commands
@@ -795,6 +857,7 @@ class CommandRegistrar:
                         project_root,
                         context_note=context_note,
                         _resolved_dir=agent_dir,
+                        link_outputs=link_outputs,
                     )
                     if registered:
                         results[agent_name] = registered
@@ -843,7 +906,7 @@ class CommandRegistrar:
                     cmd_file = (
                         target_dir / f"{output_name}{agent_config['extension']}"
                     )
-                    if cmd_file.exists():
+                    if cmd_file.exists() or cmd_file.is_symlink():
                         cmd_file.unlink()
                         # For SKILL.md agents each command lives in its own
                         # subdirectory (e.g. .agents/skills/speckit-ext-cmd/