Add guest sessions and agent VM defaults

Add daemon-backed workspace and guest-session primitives so host
orchestrators can prepare /root/repo, launch long-lived guest commands,
and attach to pipe-mode sessions over the local stdio mux bridge.

Persist richer session metadata and launch diagnostics, preflight guest
cwd/command requirements, make pipe-mode attach rehydratable from guest
state after daemon restart, and allow submodules when workspace prepare
runs in full_copy mode.

At the same time, stop vm run from auto-attaching opencode, make it
print next-step commands instead, and make glibc guest images more
agent-ready by installing node, opencode, claude, and pi while syncing
opencode/claude/pi auth files into work disks on VM start.

Validation:
- GOCACHE=/tmp/banger-gocache go test ./...
- make build
- banger vm workspace prepare --help
- banger vm session --help
- banger vm session start --help
- banger vm session attach --help

README.md

@@ -113,17 +113,45 @@ Create and use a VM:
 
 `vm create` stays synchronous by default, but on a TTY it now shows live progress until the VM is fully ready.
 
-Start a repo-backed VM session and attach `opencode` automatically:
+Start a repo-backed VM session:
 
 ```bash
 ./build/bin/banger vm run
 ./build/bin/banger vm run ../some-repo --branch feature/alpine --from HEAD
 ```
 
-`vm run` resolves the enclosing git repository, creates a VM, copies a git checkout plus current tracked and untracked non-ignored files into `/root/repo`, starts a best-effort guest tooling harness that inspects the repo and installs clearly-needed tools with `mise`, and then prefers a host-side `opencode attach` session when the local client supports it. Older host opencode clients fall back to starting `opencode` inside the guest over SSH. The harness runs asynchronously and logs its output inside the guest.
+`vm run` resolves the enclosing git repository, creates a VM, copies a git checkout plus current tracked and untracked non-ignored files into `/root/repo`, starts a best-effort guest tooling bootstrap that only uses `mise`, prints next-step commands, and exits. It does not auto-attach `opencode` anymore. The bootstrap runs asynchronously and logs its output inside the guest.
+
+After `vm run`, use one of:
+
+```bash
+./build/bin/banger vm ssh <vm-name>
+opencode attach http://<vm-name>.vm:4096 --dir /root/repo
+./build/bin/banger vm acp <vm-name>
+./build/bin/banger vm ssh <vm-name> -- "cd /root/repo && claude"
+./build/bin/banger vm ssh <vm-name> -- "cd /root/repo && pi"
+```
 
 For ACP-aware host tools, `./build/bin/banger vm acp <vm-name>` bridges stdio to guest `opencode acp` over SSH. It uses `/root/repo` when that checkout exists, otherwise `/root`, and `--cwd` lets you override the guest working directory explicitly.
 
+If you want reusable orchestration primitives instead of the `vm run` convenience flow, use the daemon-backed workspace and session commands directly:
+
+```bash
+./build/bin/banger vm workspace prepare <vm-name>
+./build/bin/banger vm workspace prepare <vm-name> ../other-repo --guest-path /root/repo --readonly
+./build/bin/banger vm session start <vm-name> --name planner --cwd /root/repo --stdin-mode pipe -- pi --mode rpc --no-session
+./build/bin/banger vm session list <vm-name>
+./build/bin/banger vm session attach <vm-name> planner
+./build/bin/banger vm session logs <vm-name> planner --stream stderr
+./build/bin/banger vm session stop <vm-name> planner
+```
+
+`vm workspace prepare` materializes a local git checkout into a running VM. The default guest path is `/root/repo` and the default mode is a shallow metadata copy plus tracked and untracked non-ignored overlay. Repositories with git submodules must use `--mode full_copy`; the metadata-based modes still reject them.
+
+`vm session start` creates a daemon-managed long-lived guest command. The daemon preflights that the requested guest `cwd` exists and that the main command, plus any repeated `--require-command` entries, exist in guest `PATH` before launch. Use `--stdin-mode pipe` when you need live `attach`; otherwise use the default detached mode and inspect sessions with `list`, `show`, `logs`, `stop`, and `kill`.
+
+`vm session attach` is currently exclusive and same-host only. The daemon exposes a local Unix socket bridge using `stdio_mux_v1`, so only one active attach is allowed at a time. Pipe-mode sessions keep enough guest-side state for the daemon to rebuild that bridge after a daemon restart.
+
 ## Web UI
 
 `bangerd` serves a local web UI by default at:
@@ -144,15 +172,25 @@ web_listen_addr = ""
 
 ## Guest Services
 
-Provisioned images include:
+Provisioned glibc-backed images include:
 
 - `banger-vsock-agent`
 - guest networking bootstrap
 - `mise`
 - `opencode`
+- `claude`
+- `pi`
 - a default guest `opencode` service on `0.0.0.0:4096`
 
-If host `~/.local/share/opencode/auth.json` exists, `banger` syncs it into the guest at `/root/.local/share/opencode/auth.json` on VM start. Changes on the host take effect after the VM is restarted.
+Alpine currently remains `opencode`-only.
+
+If these host auth files exist, `banger` syncs them into the guest on VM start:
+
+- `~/.local/share/opencode/auth.json` -> `/root/.local/share/opencode/auth.json`
+- `~/.claude/.credentials.json` -> `/root/.claude/.credentials.json`
+- `~/.pi/agent/auth.json` -> `/root/.pi/agent/auth.json`
+
+Changes on the host take effect after the VM is restarted. Session/history directories are not copied.
 
 From the host: