docs(worktrees): API reference, wiki page and the invariants behind them

Documents the worktree endpoints and quick-start's worktree field in
docs/api-reference.md, adds a Git Worktrees page to the wiki (sidebar,
Home index, a pointer from Core Concepts where sessions sharing one
case folder is explained), and records the rules that keep the feature
safe in docs/architecture-invariants.md with a short CLAUDE.md pointer:
only the managed .claude/worktrees path is ever touched, git never runs
over a Docker workspace, removal is never forced and branch delete is
-d only, and sessions start through the existing create paths.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/wiki/Core-Concepts.md

@@ -46,7 +46,8 @@ case. Each has a stable id, and that id is what the API, the wait primitives, an
 event use.
 
 Several sessions can share one case. That is the normal way to parallelize: three workers
-in the same repo, three tabs, one case.
+in the same repo, three tabs, one case. They then also share one folder; when the workers
+edit and commit in parallel, give each its own checkout with [Git Worktrees](Git-Worktrees).
 
 A session carries state the case does not:
 

docs/wiki/Git-Worktrees.md

@@ -0,0 +1,66 @@
+# Git Worktrees
+
+Sessions in one case share its folder. That is fine for one agent, but three agents in the
+same checkout edit the same files, overwrite each other's builds, and commit each other's
+half-finished work. A **git worktree** gives each of them a checkout of its own: same
+repository, same history, a separate folder on a separate branch.
+
+Codeman creates worktrees for a case whose folder is a git repository, starts sessions in
+them, and removes them again when the work is done.
+
+## Where they live
+
+`<case>/.claude/worktrees/<name>`, on a new branch `worktree-<name>`. That is exactly where
+Claude Code's own `claude --worktree <name>` puts them, so a worktree made in Codeman is one
+Claude Code recognizes, and the other way round. Codeman's Recent Sessions and Session Manager
+lists mark a session that runs in one with a `⑂ <name>` pill.
+
+The main checkout does not show the worktrees as untracked: Codeman adds `/.claude/worktrees/`
+(and `/.claude/settings.local.json`, the hooks file it writes for every Claude session) to the
+repository's local `.git/info/exclude` when git does not ignore them already. Your tracked
+`.gitignore` is never touched.
+
+## Creating one and starting a session in it
+
+1. Pick the case in the toolbar's case picker.
+2. Open the picker again and choose **Git worktrees…** (on a phone: the case sheet's
+   **Worktrees** button).
+3. Under **New worktree**, type a name (letters, digits, `.`, `_`, `-`, up to 64 characters).
+4. Pick the CLI under **Start sessions with** (Claude Code, Codex, a shell, any installed run
+   mode).
+5. **Create & start session**.
+
+The worktree is created from the case's current commit, and the session opens in it as a tab
+named `w1-<name>`. Under **Branch and start point** you can name the branch yourself or start
+from another branch, tag or commit. An existing branch is never reused or reset: pick another
+name.
+
+**Open** on a worktree's row starts another session in it, with the CLI chosen above.
+
+## Removing one
+
+Two ways, and both use `git worktree remove` **without** `--force`:
+
+- **Remove…** on the worktree's row in the dialog.
+- Closing a session that runs in a worktree: the Close Session dialog offers **Kill & remove
+  worktree**, which kills the session and then removes its worktree.
+
+git refuses to remove a worktree that still holds uncommitted or untracked files, and Codeman
+shows that refusal as git worded it and leaves everything in place. Commit, stash or delete the
+work first, then remove again. A worktree a live session still runs in is refused too.
+
+**Also delete its branch** deletes the branch with `git branch -d`, which keeps a branch whose
+commits are not merged yet. The worktree is still removed, and the message says the branch was
+kept.
+
+## What is not supported
+
+- **Docker cases and remote (SSH) cases.** A container can write to its workspace, and creating
+  a worktree runs the repository's hooks and checkout filters on the Codeman machine, so git is
+  never run there. A remote case's repository is on another machine.
+- A case folder that is not the top of a repository (a subfolder of one), a bare repository, or
+  an empty repository with no commit yet.
+- Worktrees outside `.claude/worktrees/` (made by hand with `git worktree add`) are listed, but
+  Codeman neither starts sessions in them from the dialog nor removes them.
+
+The HTTP endpoints are in the [HTTP API](HTTP-API) reference (`/api/cases/:name/worktrees`).

docs/wiki/HTTP-API.md

@@ -72,7 +72,7 @@ Roughly 235 handlers across 26 route modules. By domain:
 | ------------------- | -------- | --------------------------------------------------- |
 | System              | 56       | Status, settings, digest, updates, tunnel.           |
 | Sessions            | 34       | Create, input, terminal, wait, last response, kill.  |
-| Cases               | 34       | Create, link, clone, remote and docker cases.        |
+| Cases               | 37       | Create, link, clone, worktrees, remote and docker cases. |
 | Files               | 17       | Preview, edit, raw, attachments, path picker.        |
 | Orchestrator        | 10       | Plans and phases.                                     |
 | Ralph               | 9        | Loop control and configuration.                       |

docs/wiki/Home.md

@@ -66,6 +66,7 @@ codeman web    # then open http://localhost:3000
 | [Agent CLIs](Agent-CLIs)                   | Which agent should this session run, and how do I set it up? |
 | [Custom Model Endpoints](Custom-Model-Endpoints) | How do I point a session at my own OpenAI-compatible endpoint? |
 | [Working With Files](Working-With-Files)   | How do I read, edit, and attach files?                     |
+| [Git Worktrees](Git-Worktrees)             | How do several agents work on one repository without sharing a folder? |
 | [Input And Voice](Input-And-Voice)         | How do I talk to an agent, including by voice?             |
 | [Mobile Guide](Mobile-Guide)               | How well does this work on a phone?                        |
 | [Keyboard Shortcuts](Keyboard-Shortcuts)   | What can I drive from the keyboard?                        |

docs/wiki/_Sidebar.md

@@ -15,6 +15,7 @@
 - [Agent CLIs](Agent-CLIs)
 - [Custom Model Endpoints](Custom-Model-Endpoints)
 - [Working With Files](Working-With-Files)
+- [Git Worktrees](Git-Worktrees)
 - [Input And Voice](Input-And-Voice)
 - [Mobile Guide](Mobile-Guide)
 - [Keyboard Shortcuts](Keyboard-Shortcuts)