refactor(mcp): move chrome-devtools recipe into agents/ai.just

Encapsulate what can be encapsulated today. The justfile recipe moves from
project-root `justfile` into `agents/ai.just` (sibling to the rest of the
APM/agent dev tooling), and `shell.nix` reverts its `KOLU_CHROME_EXECUTABLE`
addition — the recipe now resolves Chrome-for-Testing inline by globbing
`$PLAYWRIGHT_BROWSERS_PATH/chromium-*/chrome-linux64/chrome`. `.mcp.json`
stays at project root (that's where Claude Code reads it from) and its
command updates to `just ai::mcp-chrome-devtools` via the existing
`mod ai 'agents/ai.just'` import.

Full encapsulation — declaring the MCP server inside `agents/apm.yml` and
letting `just ai::apm` regenerate `.mcp.json` — is blocked on
microsoft/apm#655 (Claude Code MCP adapter) landing in juspay's fork. The
follow-up TODO is captured in the recipe's doc comment.

Trade-off: the hickey-iteration's elegant Nix-eval-time chrome-path
resolution (read browsers.json at eval, fail loud on layout change) is
dropped in favor of a runtime shell glob. Failure mode shifts from
"fails at `nix develop` eval" to "empty --executable-path at MCP startup
→ chrome-devtools-mcp errors out loud" — different failure point, still
loud, and keeps `shell.nix` free of MCP-specific env vars.

Author: srid

.mcp.json

@@ -2,7 +2,7 @@
   "mcpServers": {
     "chrome-devtools": {
       "command": "nix",
-      "args": ["develop", "--command", "just", "mcp-chrome-devtools"]
+      "args": ["develop", "--command", "just", "ai::mcp-chrome-devtools"]
     }
   }
 }

agents/ai.just

@@ -61,3 +61,16 @@ apm-sync: apm-audit
 agent *args: apm
     just prepare
     {{ env('AI_AGENT', 'claude --dangerously-skip-permissions') }} {{ args }}
+
+# Launch chrome-devtools-mcp server over stdio — wired up via the root
+# `.mcp.json`, which shells out via `nix develop --command just
+# ai::mcp-chrome-devtools` (Claude Code starts outside the nix devshell).
+# Chrome binary resolved from Playwright's nix-provided Chrome-for-Testing;
+# glob misses fail loud downstream (empty --executable-path → MCP server
+# errors out visibly). Headless Linux only.
+#
+# TODO: fold .mcp.json's entry into `dependencies.mcp` above once
+# microsoft/apm#655 (Claude Code MCP adapter) merges and lands in juspay's
+# fork — `.mcp.json` then becomes a generated artifact of `just ai::apm`.
+mcp-chrome-devtools:
+    sh -c 'chrome="$(ls -d "$PLAYWRIGHT_BROWSERS_PATH"/chromium-*/chrome-linux64/chrome 2>/dev/null | head -1)"; exec npx -y chrome-devtools-mcp@latest --headless=true --isolated=true --executable-path="$chrome"'

justfile

@@ -95,18 +95,6 @@ fmt:
 fmt-check:
     {{ nix_shell }} sh -c 'prettier --check --cache --ignore-unknown . && nixpkgs-fmt --check *.nix nix/**/*.nix'
 
-# Launch chrome-devtools-mcp server over stdio — wired up via .mcp.json.
-# Drives Playwright's nix-provided Chrome-for-Testing (headless, isolated
-# profile). Claude Code starts outside the devshell, so .mcp.json wraps
-# this with `nix develop --command just mcp-chrome-devtools`.
-#
-# TODO: fold this + .mcp.json into agents/apm.yml's `dependencies.mcp` once
-# microsoft/apm#655 (Claude Code MCP adapter) merges and lands in juspay's
-# fork — then the recipe moves into agents/ai.just and .mcp.json becomes a
-# generated artifact.
-mcp-chrome-devtools:
-    {{ nix_shell }} sh -c 'exec npx -y chrome-devtools-mcp@latest --headless=true --isolated=true --executable-path="$KOLU_CHROME_EXECUTABLE"'
-
 # Nix build (server + client)
 build:
     nix build

shell.nix

@@ -2,17 +2,6 @@
 { pkgs ? import ./nix/nixpkgs.nix { } }:
 let
   packages = import ./default.nix { inherit pkgs; };
-
-  # Chrome-for-Testing path for chrome-devtools-mcp (see .mcp.json). Pulled
-  # from playwright-driver's browsers.json at eval time so the chromium-N
-  # revision tracks whatever nixpkgs pins — fails loud here if layout changes
-  # instead of silently at MCP startup. Idiom from https://wiki.nixos.org/wiki/Playwright.
-  playwrightBrowsers = (builtins.fromJSON
-    (builtins.readFile "${pkgs.playwright-driver}/browsers.json")).browsers;
-  chromiumRev = (builtins.head
-    (builtins.filter (b: b.name == "chromium") playwrightBrowsers)).revision;
-  koluChromeExecutable =
-    "${pkgs.playwright-driver.browsers}/chromium-${chromiumRev}/chrome-linux64/chrome";
 in
 pkgs.mkShell {
   name = "kolu-shell";
@@ -22,7 +11,6 @@ pkgs.mkShell {
     KOLU_COMMIT_HASH = "dev";
     PLAYWRIGHT_BROWSERS_PATH = "${pkgs.playwright-driver.browsers}";
     PLAYWRIGHT_SKIP_BROWSER_DOWNLOAD = "1";
-    KOLU_CHROME_EXECUTABLE = koluChromeExecutable;
   };
 
   shellHook = ''