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/agent.go

@@ -57,6 +57,8 @@ func workspaceAgent() *serpent.Command {
 		devcontainers                  bool
 		devcontainerProjectDiscovery   bool
 		devcontainerDiscoveryAutostart bool
+		socketServerEnabled            bool
+		socketPath                     string
 	)
 	agentAuth := &AgentAuth{}
 	cmd := &serpent.Command{
@@ -317,6 +319,8 @@ func workspaceAgent() *serpent.Command {
 						agentcontainers.WithProjectDiscovery(devcontainerProjectDiscovery),
 						agentcontainers.WithDiscoveryAutostart(devcontainerDiscoveryAutostart),
 					},
+					SocketPath:          socketPath,
+					SocketServerEnabled: socketServerEnabled,
 				})
 
 				if debugAddress != "" {
@@ -477,6 +481,19 @@ func workspaceAgent() *serpent.Command {
 			Description: "Allow the agent to autostart devcontainer projects it discovers based on their configuration.",
 			Value:       serpent.BoolOf(&devcontainerDiscoveryAutostart),
 		},
+		{
+			Flag:        "socket-server-enabled",
+			Default:     "false",
+			Env:         "CODER_AGENT_SOCKET_SERVER_ENABLED",
+			Description: "Enable the agent socket server.",
+			Value:       serpent.BoolOf(&socketServerEnabled),
+		},
+		{
+			Flag:        "socket-path",
+			Env:         "CODER_AGENT_SOCKET_PATH",
+			Description: "Specify the path for the agent socket.",
+			Value:       serpent.StringOf(&socketPath),
+		},
 	}
 	agentAuth.AttachOptions(cmd, false)
 	return cmd