feat(ssh): discover computers from ~/.ssh/known_hosts + remote system-prompt

Two improvements to the SSH support feature:

1. KNOWN_HOSTS DISCOVERY (packages/ssh):
   Computers are now auto-discovered from ~/.ssh/known_hosts (every hostname
   you've ever connected to) in ADDITION to ~/.ssh/config (explicit Host
   aliases). Config entries take precedence (full params); known_hosts entries
   get defaulted params (User=defaultUser, IdentityFile=null→pool probes
   default keys, Port from [host]:port or 22, knownHost=true). Zero-config —
   no ~/.ssh/config file needed; hosts just appear.

   Reject list: dispatch.toml [ssh].reject = [...] (glob patterns like
   github.com, *.ts.net) filters noise from the catalog. Read from both
   the global ~/.config/dispatch/dispatch.toml and the project dispatch.toml.
   Parsed with Bun.TOML.parse (zero deps). Only filters discovery (catalog);
   specific lookups (getComputer/getStatus/test/connect) ignore the reject
   list (it's a visibility filter, not access control).

   New pure functions: parseKnownHosts(), isRejected(), globMatch().
   +26 tests. tsc EXIT 0, biome clean, 1756 tests pass.

2. REMOTE SYSTEM-PROMPT AWARENESS (packages/system-prompt):
   When a conversation has a computerId set (remote turn), the system prompt
   now resolves system:os, system:hostname, git:branch/git:status, and
   file: reads against the REMOTE machine — not the local host. Previously
   the prompt always said 'Arch Linux (WSL)' + local hostname even when the
   agent was connected to a remote Artix Linux machine.

   The ResolverAdapters' hostname()/platform() are now async (so a remote
   adapter can run 'hostname'/'uname -s' over SSH). The system-prompt
   extension builds remote adapters from the ExecBackend (readFile→SFTP,
   spawn→SSH exec). Cache invalidation now checks computerId (switching
   computers rebuilds the prompt). The compaction path also threads
   computerId. @dispatch/system-prompt now depends on @dispatch/exec-backend.

1 files changed, 9 insertions, 9 deletions

diff --git a/packages/system-prompt/src/resolver.test.ts b/packages/system-prompt/src/resolver.test.ts
index 474c79a..d55af07 100644
--- a/packages/system-prompt/src/resolver.test.ts
+++ b/packages/system-prompt/src/resolver.test.ts
@@ -37,8 +37,8 @@ describe("resolver", () => {
 				spawn: failSpawn(),
 				fs: fakeFs(new Map()),
 				now: () => fixedNow,
-				platform: () => "linux",
-				hostname: () => "myhost",
+				platform: async () => "linux",
+				hostname: async () => "myhost",
 			});
 
 			expect(map.get("system:time")).toBe("2024-06-15T12:30:00.000Z");
@@ -83,7 +83,7 @@ describe("resolver", () => {
 			const map = await resolveVariables("/proj", {
 				spawn: failSpawn(),
 				fs: fakeFs(files),
-				platform: () => "linux",
+				platform: async () => "linux",
 			});
 			expect(map.get("system:os")).toBe("Ubuntu 22.04 LTS");
 		});
@@ -95,7 +95,7 @@ describe("resolver", () => {
 			const map = await resolveVariables("/proj", {
 				spawn: failSpawn(),
 				fs: fakeFs(files),
-				platform: () => "linux",
+				platform: async () => "linux",
 			});
 			expect(map.get("system:os")).toBe("Debian 12");
 		});
@@ -108,7 +108,7 @@ describe("resolver", () => {
 			const map = await resolveVariables("/proj", {
 				spawn: failSpawn(),
 				fs: fakeFs(files),
-				platform: () => "linux",
+				platform: async () => "linux",
 			});
 			expect(map.get("system:os")).toBe("Ubuntu 22.04 LTS (WSL)");
 		});
@@ -121,7 +121,7 @@ describe("resolver", () => {
 			const map = await resolveVariables("/proj", {
 				spawn: failSpawn(),
 				fs: fakeFs(files),
-				platform: () => "linux",
+				platform: async () => "linux",
 			});
 			expect(map.get("system:os")).toBe("Ubuntu 22.04 LTS (WSL)");
 		});
@@ -131,7 +131,7 @@ describe("resolver", () => {
 			const map = await resolveVariables("/proj", {
 				spawn: failSpawn(),
 				fs: fakeFs(files),
-				platform: () => "linux",
+				platform: async () => "linux",
 			});
 			expect(map.get("system:os")).toBe("Linux (WSL)");
 		});
@@ -140,7 +140,7 @@ describe("resolver", () => {
 			const map = await resolveVariables("/proj", {
 				spawn: failSpawn(),
 				fs: fakeFs(new Map()),
-				platform: () => "linux",
+				platform: async () => "linux",
 			});
 			expect(map.get("system:os")).toBe("linux");
 		});
@@ -149,7 +149,7 @@ describe("resolver", () => {
 			const map = await resolveVariables("/proj", {
 				spawn: failSpawn(),
 				fs: fakeFs(new Map()),
-				platform: () => "darwin",
+				platform: async () => "darwin",
 			});
 			expect(map.get("system:os")).toBe("darwin");
 		});