[cryptotavares]

Summary: Every mm call now costs about 0.1 s of CLI time instead of 0.23 s, and a browser daemon no longer loads @metamask/device-mcp. The README tells agents to call node_modules/.bin/mm, because yarn mm adds another 0.35-0.45 s per call.

Stack context: mm CLI v2, Phase 1, P1-25 (first Tier 1 ticket after the stack merge). Base: main.

Problem

Measured on main 227674a, daemon running, p50 of 10:

Per call	ms
node -e 0	65
node_modules/.bin/mm status	227
yarn mm status	574 (Extension) / 702 (Mobile)

• resolveWorktreeRoot (src/cli/mm.ts:270) runs git rev-parse --show-toplevel on every call: about 90 ms.
• The CLI imports observeLevelSchema from validation/schemas.ts only to read three strings. That loads zod: 79 of the CLI's 95 modules, about 25 ms.
• MobilePlatformDriver imports device-mcp at module load, and src/index.ts re-exports it, so every browser daemon loads 54 device-mcp modules at start.
• The README says to use yarn mm. On a 400-call release run, yarn alone is about 2.5-3 minutes.

Solution

Change	Where
Walk up from the real cwd to the nearest .git entry (directory or file). Fall back to git rev-parse when there is none, or when GIT_DIR / GIT_WORK_TREE is set	findGitWorktreeRoot in src/cli/mm.ts
Move the observe levels to a zod-free module; schemas.ts builds its enum from it	src/validation/observe-level.ts
Load device-mcp on first use: require in the CJS build (shares the consumer's copy), import() in the ESM build. The Hermes session is created on first use	src/platform/device-mcp-runtime.ts, mobile-platform-driver.ts
Recommend node_modules/.bin/mm for agents, with the measured cost	README.md

Outcome

Before = main, after = this branch, same host, back to back. No device is touched by the bench.

Metric	App	Before p50 ms	After p50 ms
node_modules/.bin/mm status	Extension	227	99
node_modules/.bin/mm status	Mobile	227	98
yarn mm status	Extension	574	439
yarn mm status	Mobile	702	564
mm --help	both	93-95	61-62
Daemon start, 8 interleaved rounds	Extension	3943	3704
Daemon start, 8 interleaved rounds	Mobile	1013	878
CLI modules loaded		95	15
device-mcp modules in a browser daemon	Extension	54	0

Decisions

Decision	Why	Rejected
require in CJS, import() in ESM	Native import() in the CJS build loads device-mcp's ESM build as a second copy next to the consumer's CJS copy. Module state (for example getHermesSession()) would split	import() everywhere; createRequire (works, but adds a shim for no gain)
Keep the git rev-parse fallback	Covers GIT_DIR / GIT_WORK_TREE setups and unusual layouts at no cost to the normal path	Removing git entirely
.git file counts as a root	Linked worktrees (our own setup) and submodules have a .git file; git rev-parse --show-toplevel returns that directory too	Directory-only check

Review guide

1. src/platform/device-mcp-runtime.ts and its test: the test fails on main ("expected true to be false") and passes here.
2. src/platform/mobile-platform-driver.ts: the four call sites that now load device-mcp (#hermesCdp, hermesTargets, generateLocators, #getHermesSession). Types stay import type.
3. findGitWorktreeRoot in src/cli/mm.ts and its tests.
4. The Hermes tests now mock ./device-mcp-runtime.js, because vi.mock('@metamask/device-mcp') does not intercept a CJS require.

Breaking changes

None. MobilePlatformDriver's public API is unchanged.

Consumer impact

Consumer	Change needed	Done on branch
Extension test/e2e/playwright/llm-workflow/	None	n/a
Mobile tests/llm-workflow/	Docs only: mention node_modules/.bin/mm	cryptotavares/mm-cli-v2-mobile 66a504511f0

Testing details

Yalc build of this branch (0.12.0+e92d761d):

• Extension e2e context (fake wallet, headless): launch, unlock, describe-screen, get-state, list-testids, cdp, screenshot. All exit 0.
• iOS simulator (dev client), read-only: launch, unlock, list-testids (wallet-screen), describe-screen, cdp Runtime.evaluate 1+1 = 2, screenshot. All exit 0. cdp goes through the lazily loaded device-mcp.
• Real Node: require('dist/index.cjs') loads 0 device-mcp modules. The first generateLocators() loads 54, the same copy as the consumer's require('@metamask/device-mcp'). import('dist/index.mjs') works through import().

 Test Files  54 passed (54)
      Tests  1844 passed (1844)
All files          |   97.55 |    94.94 |   96.75 |   97.69 |

yarn lint passes. attw --pack is green for node10, node16 CJS, node16 ESM and bundler. Coverage thresholds are unchanged.