#3427 Docs: swamp workspace commands and workspaces in the manual (swamp-club#3424)

Follow-up to swamp-club#3424 (swamp PR #3093, merged 2026-10-14). The manual has no page about workspaces or swamp start yet. Suggested new page: content/manual/reference/workspace-commands.md, following the invite-commands.md and issue-commands.md pattern. Design source: design/surfaces/workspace.md in the swamp repo.

1. What a workspace is. A swamp repo that Swamp keeps track of in the workspace registry, /workspaces.json (moves with SWAMP_CONFIG_DIR and SWAMP_HOME). Two kinds: created workspaces live under /workspaces/ (~/.swamp/workspaces by default) with no agent set up; imported workspaces are existing repos registered where they are, with nothing moved or copied. A workspace is still an ordinary repo, so every other command works in it unchanged.

2. The commands, each in log and JSON mode:

• swamp workspace create : names are lowercase letters, digits and dashes, at most 63 characters. Errors: name_taken, folder_exists (a folder registered under another name, or a repo folder left behind by remove; the message gives the import command), not_a_workspace (the folder holds something else).
• swamp workspace import [--name ]: the default name is made from the folder name (lowercased, dashes), with a -2, -3 suffix on a clash. Importing a folder that is already registered succeeds and reports its existing name (alreadyRegistered: true in JSON). Errors: not_found, not_a_repo, name_taken.
• swamp workspace list: every registered workspace by name, marking imported ones and folders that are missing or no longer a swamp repo (folder: ok, missing or not_a_repo in JSON). Writes nothing.
• swamp workspace get : path, created time, imported, trusted, enrolled agents, and whether a swamp start has it open. Writes nothing.
• swamp workspace remove : takes the workspace off the registry and drops the agent trust recorded for its folder. The folder is never deleted; the output gives the import command that brings it back, and trust has to be confirmed again after re-importing.

1. Upgrading from earlier swamp start. Folders swamp start created before the registry existed are adopted the first time a command that writes the registry runs; list and get report them without writing anything.

2. Relationship to swamp start. swamp start and swamp workspace share the same registry and folders: a workspace created or imported by either shows up in the other, and swamp start status lists the same workspaces. Known gap to mention or leave out: swamp start --workspace currently re-registers a removed workspace folder without saying so.

3. Cross-links. Link the new page from the CLI reference index and from the install or getting-started page wherever swamp start is introduced. swamp start itself has no manual page yet; if one is added, it should link here.