feat(build.py): --no-purge flag and opencode-archive install target

Conflict fix: --install opencode wipes ~/.config/opencode/skills/ on every
build, which clobbers the work of external managers like opc-skills. New flag
--no-purge skips that wipe so opc-skills' enabled set survives a rebuild.

New install target opencode-archive: instead of writing to ~/.config/opencode/,
it regenerates personas/skills-archive/ + personas/agents-opencode-archive/
(the source-of-truth that opc-skills + opc-agents consume). This lets the
build pipeline stay decoupled from runtime install dirs.

install_opencode() now accepts agents_dest / skills_dest overrides for the
archive target. Live target behavior unchanged.

build.py

@@ -1513,6 +1513,9 @@ def install_opencode(
     output_dir: Path,
     shared_dir: Path | None = None,
     topics: set[str] | None = None,
+    purge_skills: bool = True,
+    agents_dest: Path | None = None,
+    skills_dest: Path | None = None,
 ):
     """Install personas to OpenCode as agents + skills.
 
@@ -1529,11 +1532,26 @@ def install_opencode(
     Args:
       topics: set of topics to install (see OPENCODE_TOPICS). Defaults to
         OPENCODE_DEFAULT_TOPICS which drops marketing/biz skills.
+      purge_skills: when True (default), wipe ~/.config/opencode/skills/
+        before installing. Set False (via --no-purge) when this dir is also
+        managed by an external tool (e.g. opc-skills) — purge would otherwise
+        delete its work on every build.
     """
     if topics is None:
         topics = OPENCODE_DEFAULT_TOPICS
-    agents_dir = Path.home() / ".config" / "opencode" / "agents"
+    # Archive mode: agents_dest / skills_dest override the live opencode dirs.
-    skills_dir = Path.home() / ".config" / "opencode" / "skills"
+    # Used by --install opencode-archive to regenerate the personas archive
+    # that opc-skills and opc-agents consume as source-of-truth.
+    if agents_dest is not None:
+        agents_dir = agents_dest
+        agents_dir.mkdir(parents=True, exist_ok=True)
+    else:
+        agents_dir = Path.home() / ".config" / "opencode" / "agents"
+    if skills_dest is not None:
+        skills_dir = skills_dest
+        skills_dir.mkdir(parents=True, exist_ok=True)
+    else:
+        skills_dir = Path.home() / ".config" / "opencode" / "skills"
     agents_dir.mkdir(parents=True, exist_ok=True)
     skills_dir.mkdir(parents=True, exist_ok=True)
 
@@ -1719,12 +1737,16 @@ def install_opencode(
     skipped_topic = 0
 
     # Purge existing skills dir so stale filtered-out skills are removed.
-    if skills_dir.exists():
+    # Skipped when --no-purge is passed (so external tools like opc-skills
+    # that manage this directory don't get clobbered on every build).
+    if purge_skills and skills_dir.exists():
         import shutil as _shutil
 
         for existing in skills_dir.iterdir():
             if existing.is_dir():
                 _shutil.rmtree(existing)
+    elif not purge_skills:
+        print(f"  OpenCode: --no-purge — preserving existing {skills_dir}/")
 
     if shared_dir:
         for skills_subdir in [
@@ -2107,12 +2129,16 @@ def main():
             "gemini",
             "openclaw",
             "opencode",
+            "opencode-archive",
             "paperclip",
             "all",
         ],
         help="Install generated personas to a target platform. "
         "'claude' installs persona agents+commands; 'claude-skills' installs "
-        "shared skills to ~/.claude/skills/ with category filters.",
+        "shared skills to ~/.claude/skills/ with category filters; "
+        "'opencode-archive' writes opencode-format agents+skills to "
+        "personas/agents-opencode-archive/ + personas/skills-archive/ "
+        "(consumed by opc-skills/opc-agents) without touching ~/.config/opencode/.",
     )
     # --- claude-skills filters --------------------------------------------
     parser.add_argument(
@@ -2171,6 +2197,13 @@ def main():
         "business-pm, uncategorized. "
         "Default drops marketing/biz. Use 'all' for no filter.",
     )
+    parser.add_argument(
+        "--no-purge",
+        action="store_true",
+        help="For --install opencode: do NOT wipe ~/.config/opencode/skills/ "
+        "before installing. Use when the directory is also managed by an "
+        "external tool (e.g. opc-skills) so its enabled skills are preserved.",
+    )
     parser.add_argument(
         "--search",
         type=str,
@@ -2325,7 +2358,7 @@ def main():
                 install_gemini(output_dir)
             elif target == "openclaw":
                 install_openclaw(output_dir)
-            elif target == "opencode":
+            elif target in ("opencode", "opencode-archive"):
                 if args.opencode_topics:
                     if args.opencode_topics.strip().lower() == "all":
                         oc_topics = OPENCODE_TOPICS
@@ -2337,7 +2370,29 @@ def main():
                         }
                 else:
                     oc_topics = None  # use default
-                install_opencode(output_dir, shared_dir, topics=oc_topics)
+                if target == "opencode-archive":
+                    # Source-of-truth layout consumed by opc-skills + opc-agents:
+                    #   personas/skills-archive/<name>/SKILL.md   ← opc-skills reads
+                    #   personas/agents-opencode-archive/<n>.md   ← opc-agents reads
+                    install_opencode(
+                        output_dir,
+                        shared_dir,
+                        topics=oc_topics,
+                        purge_skills=False,
+                        agents_dest=root / "agents-opencode-archive",
+                        skills_dest=root / "skills-archive",
+                    )
+                    print(
+                        "  opcode-archive: regenerated source-of-truth used by "
+                        "opc-skills + opc-agents. Did NOT touch ~/.config/opencode/."
+                    )
+                else:
+                    install_opencode(
+                        output_dir,
+                        shared_dir,
+                        topics=oc_topics,
+                        purge_skills=not args.no_purge,
+                    )
             elif target == "paperclip":
                 install_paperclip(output_dir, personas_dir, shared_dir)