feat: implement agent socket api, client and cli (#20758)

closes: https://github.com/coder/coder/issues/10352
closes: https://github.com/coder/internal/issues/1094
closes: https://github.com/coder/internal/issues/1095

In this pull request, we enable a new set of experimental cli commands
grouped under `coder exp sync`.
These commands allow any process acting within a coder workspace to
inform the coder agent of its requirements and execution progress. The
coder agent will then relay this information to other processes that
have subscribed.

These commands are:
```
# Check if this feature is enabled in your environment 
coder exp sync ping

# express that your unit depends on another
coder exp sync want <unit> <dependency_unit> 

# express that your unit intends to start a portion of the script that requires 
# other units to have completed first. This command blocks until all dependencies have been met
coder exp sync start <unit> 

# express that your unit has completes its work, allowing dependent units to begin their execution
coder exp sync complete <unit>
```

Example:

In order to automatically run claude code in a new workspace, it must
first have a git repository cloned. The scripts responsible for cloning
the repository and for running claude code would coordinate in the
following way:

```bash
# Script A: Claude code

# Inform the agent that the claude script wants the git script.
# That is, the git script must have completed before the claude script can begin its execution
coder exp sync want claude git

# Inform the agent that we would now like to begin execution of claude.
# This command will block until the git script (and any other defined dependencies)
# have completed
coder exp sync start claude

# Now we run claude code and any other commands we need
claude ...

# Once our script has completed, we inform the agent, so that any scripts that depend on this one
# may begin their execution

coder exp sync complete claude
```

```bash
# Script B: Git

# Because the git script does not have any dependencies, we can simply inform the agent that we 
# intend to start
coder exp sync start git

git clone ssh://git@github.com/coder/coder

# Once the repository have been cloned, we inform the agent that this script is complete, so that
# scripts that depend on it may begin their execution.
coder exp sync complete git
```

Notes:
* Unit names (ie. `claude` and `git`) given as input to the sync
commands are arbitrary strings. You do not have to conform to specific
identifiers. We recommend naming your scripts descriptively, but
succinctly.
* Scripts unit names should be well documented. Other scripts will need
to know the names you've chosen in order to depend on yours. Therefore,
you

---------

Co-authored-by: Mathias Fredriksson <mafredri@gmail.com>

cli/sync_complete.go

@@ -0,0 +1,47 @@
+package cli
+
+import (
+	"golang.org/x/xerrors"
+
+	"github.com/coder/coder/v2/agent/agentsocket"
+	"github.com/coder/coder/v2/agent/unit"
+	"github.com/coder/coder/v2/cli/cliui"
+	"github.com/coder/serpent"
+)
+
+func (*RootCmd) syncComplete(socketPath *string) *serpent.Command {
+	cmd := &serpent.Command{
+		Use:   "complete <unit>",
+		Short: "Mark a unit as complete",
+		Long:  "Mark a unit as complete. Indicating to other units that it has completed its work. This allows units that depend on it to proceed with their startup.",
+		Handler: func(i *serpent.Invocation) error {
+			ctx := i.Context()
+
+			if len(i.Args) != 1 {
+				return xerrors.New("exactly one unit name is required")
+			}
+			unit := unit.ID(i.Args[0])
+
+			opts := []agentsocket.Option{}
+			if *socketPath != "" {
+				opts = append(opts, agentsocket.WithPath(*socketPath))
+			}
+
+			client, err := agentsocket.NewClient(ctx, opts...)
+			if err != nil {
+				return xerrors.Errorf("connect to agent socket: %w", err)
+			}
+			defer client.Close()
+
+			if err := client.SyncComplete(ctx, unit); err != nil {
+				return xerrors.Errorf("complete unit failed: %w", err)
+			}
+
+			cliui.Info(i.Stdout, "Success")
+
+			return nil
+		},
+	}
+
+	return cmd
+}