fix(skills): validate skill names and quote provisioning paths

Skill names become host/guest path segments interpolated into the
`bottle.exec` shell strings in each contrib provider's provision_skills.
They were validated only as strings, so a name with shell metacharacters
or path traversal could reach the command.

Layer two defenses:
  - Primary: reject any skill name that isn't kebab-case
    ([a-z][a-z0-9-]*) at manifest load, reusing the convention already
    enforced on bottle/agent filenames (new is_valid_entity_name helper
    in manifest_schema). Fails loud and early, protecting every consumer
    of the name — not just the exec call sites.
  - Failsafe: shlex.quote the interpolated skills_dir / dst paths in the
    claude, codex, and pi providers, so a future unvalidated field can't
    inject shell metacharacters even if it bypasses the load-time check.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NkwFXLFff9PYPy4wgVBJp9

bot_bottle/contrib/claude/agent_provider.py

@@ -217,7 +217,7 @@ class ClaudeAgentProvider(AgentProvider):
         if not agent.skills:
             return
         skills_dir = _skills_dir(plan.guest_home)
-        bottle.exec(f"mkdir -p {skills_dir}", user="root")
+        bottle.exec(f"mkdir -p {shlex.quote(skills_dir)}", user="root")
         for name in agent.skills:
             src = host_skill_dir(name)
             if not os.path.isdir(src):
@@ -227,9 +227,13 @@ class ClaudeAgentProvider(AgentProvider):
                 )
             dst = f"{skills_dir}/{name}"
             info(f"copying skill {name} into {bottle.name}:{dst}")
-            bottle.exec(f"rm -rf {dst} && mkdir -p {dst}", user="root")
+            # Defense in depth: skill names are validated kebab-case at
+            # manifest load, but quote the path so a future unvalidated
+            # field can't inject shell metacharacters here either.
+            dst_q = shlex.quote(dst)
+            bottle.exec(f"rm -rf {dst_q} && mkdir -p {dst_q}", user="root")
             bottle.cp_in(f"{src}/.", f"{dst}/")
-            bottle.exec(f"chown -R node:node {dst}", user="root")
+            bottle.exec(f"chown -R node:node {dst_q}", user="root")
 
     def provision_prompt(self, plan: "BottlePlan", bottle: "Bottle") -> str | None:
         """Copy the prompt file into the guest, fix ownership/mode.

bot_bottle/contrib/codex/agent_provider.py

@@ -183,7 +183,7 @@ class CodexAgentProvider(AgentProvider):
         if not agent.skills:
             return
         skills_dir = _skills_dir(plan.guest_home)
-        bottle.exec(f"mkdir -p {skills_dir}", user="root")
+        bottle.exec(f"mkdir -p {shlex.quote(skills_dir)}", user="root")
         for name in agent.skills:
             src = host_skill_dir(name)
             if not os.path.isdir(src):
@@ -193,9 +193,13 @@ class CodexAgentProvider(AgentProvider):
                 )
             dst = f"{skills_dir}/{name}"
             info(f"copying skill {name} into {bottle.name}:{dst}")
-            bottle.exec(f"rm -rf {dst} && mkdir -p {dst}", user="root")
+            # Defense in depth: skill names are validated kebab-case at
+            # manifest load, but quote the path so a future unvalidated
+            # field can't inject shell metacharacters here either.
+            dst_q = shlex.quote(dst)
+            bottle.exec(f"rm -rf {dst_q} && mkdir -p {dst_q}", user="root")
             bottle.cp_in(f"{src}/.", f"{dst}/")
-            bottle.exec(f"chown -R node:node {dst}", user="root")
+            bottle.exec(f"chown -R node:node {dst_q}", user="root")
 
     def provision_prompt(self, plan: "BottlePlan", bottle: "Bottle") -> str | None:
         """Copy the prompt file into the guest, fix ownership/mode.

bot_bottle/contrib/pi/agent_provider.py

@@ -238,7 +238,7 @@ class PiAgentProvider(AgentProvider):
         if not agent.skills:
             return
         skills_dir = _skills_dir(plan.guest_home)
-        bottle.exec(f"mkdir -p {skills_dir}", user="root")
+        bottle.exec(f"mkdir -p {shlex.quote(skills_dir)}", user="root")
         for name in agent.skills:
             src = host_skill_dir(name)
             if not os.path.isdir(src):
@@ -248,9 +248,13 @@ class PiAgentProvider(AgentProvider):
                 )
             dst = f"{skills_dir}/{name}"
             info(f"copying skill {name} into {bottle.name}:{dst}")
-            bottle.exec(f"rm -rf {dst} && mkdir -p {dst}", user="root")
+            # Defense in depth: skill names are validated kebab-case at
+            # manifest load, but quote the path so a future unvalidated
+            # field can't inject shell metacharacters here either.
+            dst_q = shlex.quote(dst)
+            bottle.exec(f"rm -rf {dst_q} && mkdir -p {dst_q}", user="root")
             bottle.cp_in(f"{src}/.", f"{dst}/")
-            bottle.exec(f"chown -R node:node {dst}", user="root")
+            bottle.exec(f"chown -R node:node {dst_q}", user="root")
 
     def provision_prompt(self, plan: "BottlePlan", bottle: "Bottle") -> str | None:
         prompt_path = _prompt_path(plan.guest_home)