refactor: move guest_home onto AgentProvisionPlan as source of truth

guest_home is now a field on AgentProvisionPlan (set by each provider's
provision_plan() method). BottlePlan.guest_home becomes a read-only
property delegating to agent_provision.guest_home so existing callers
(provision_git, provision_skills, provision_prompt) are unchanged.

Both resolve_plan.py files drop guest_home from the plan constructor
call; the local variable still exists as an intermediary for the
workspace_plan call that precedes agent_provision_plan.

bot_bottle/agent_provider.py

@@ -103,6 +103,7 @@ class AgentProvisionPlan:
     prompt_mode: PromptMode
     image: str
     dockerfile: str
+    guest_home: str
     guest_env: dict[str, str]
     env_vars: dict[str, str] = field(default_factory=dict)
     dirs: tuple[AgentProvisionDir, ...] = ()

bot_bottle/backend/__init__.py

@@ -78,9 +78,12 @@ class BottlePlan(ABC):
 
     spec: BottleSpec
     stage_dir: Path
-    guest_home: str
     git_gate_plan: GitGatePlan
 
+    @property
+    def guest_home(self) -> str:
+        return self.agent_provision.guest_home
+
     @property
     def git_gate_insteadof_host(self) -> str:
         """Host (and optional port) used in git-gate insteadOf URLs.

bot_bottle/backend/docker/resolve_plan.py

@@ -169,7 +169,6 @@ def resolve_plan(
     return DockerBottlePlan(
         spec=spec,
         stage_dir=stage_dir,
-        guest_home=guest_home,
         slug=slug,
         container_name=container_name,
         container_name_pinned=container_name_pinned,

bot_bottle/backend/smolmachines/resolve_plan.py

@@ -114,7 +114,6 @@ def resolve_plan(
     return SmolmachinesBottlePlan(
         spec=spec,
         stage_dir=stage_dir,
-        guest_home=guest_home,
         slug=slug,
         bundle_subnet=subnet,
         bundle_gateway=gateway,

bot_bottle/contrib/claude/agent_provider.py

@@ -110,6 +110,7 @@ class ClaudeAgentProvider(AgentProvider):
             prompt_mode=_RUNTIME.prompt_mode,
             image=_RUNTIME.image,
             dockerfile=dockerfile,
+            guest_home=guest_home,
             env_vars=env_vars,
             guest_env=resolved_guest_env,
             files=files,

bot_bottle/contrib/codex/agent_provider.py

@@ -147,6 +147,7 @@ class CodexAgentProvider(AgentProvider):
             prompt_mode=_RUNTIME.prompt_mode,
             image=_RUNTIME.image,
             dockerfile=dockerfile,
+            guest_home=guest_home,
             env_vars=env_vars,
             guest_env=resolved_guest_env,
             dirs=tuple(dirs),