# Where the time actually goes in an AI coding-agent job

> Source: <https://dev.to/arti0/where-the-time-actually-goes-in-an-ai-coding-agent-job-13ei>
> Published: 2026-08-15 14:16:18+00:00

I run an agent-orchestration platform: it takes a ticket, spins up a git worktree, lets a Claude Code agent build the feature, and runs a deterministic verify gate before merging. A typical job takes 20–30 minutes.

I used to blame slow model responses for the runtime, but stage-by-stage measurements proved that assumption wrong: **infrastructure overhead costs 5–8 minutes of every job before the agent even finishes.**

Here is where the time actually goes and how to optimize it.

On a standard dev machine (Windows 11, Bun, Next.js), a single job pays a heavy infrastructure tax:

| Stage | Measured Cost | Impact / Notes |
|---|---|---|
`git worktree add` |
Seconds | Negligible overhead. |
`bun install` |
~91s (median) |
Cold worktree setup, even with a warm cache. |
Lint & Typecheck |
~1–2 minutes |
`eslint` + 2× `tsc` across the full repo with no shared cache. |
`next build` |
Minutes |
The longest gate leg due to a cold `.next` directory every run. |
Vitest |
~26 seconds | Fast and acceptable. |
Model Time |
~15–22 minutes | Planning, execution, and review calls. |

Fixed infrastructure costs account for **20% to 30% of total runtime**. Eliminating this overhead reduces small job times from ~30 minutes to ~20 minutes, leaving the remaining time strictly bounded by model inference.

Instead of creating a fresh worktree and running `bun install`

from scratch for every job, maintain a small pool of pre-warmed directories containing:

`node_modules`

directory (invalidated only when the lockfile hash changes).`.next`

, `tsconfig.tsbuildinfo`

, `.eslintcache`

).When a job starts, it claims a slot, checks out the target branch, and immediately executes. After completion, `git clean`

resets the worktree while leaving cache directories intact. This eliminates the ~91-second install step on almost every job.

Next.js supports persistent filesystem build caching. Combining this with a warm slot pool carries the `.next`

cache between jobs, turning the longest gate step from minutes into tens of seconds for standard diffs.

Adding `--incremental`

to `tsc`

and `--cache`

to `eslint`

within the persistent slot directory saves roughly 1 minute per job without changing verification outcomes.

Real-time Defender scanning severely throttles small-file I/O operations (like `node_modules`

and `.next`

writes). Adding directory exclusions or moving worktrees to a **ReFS Dev Drive** improves install and build I/O speeds by 2× to 5× with zero code changes.

Switching to `bun install --linker isolated`

provides pnpm-style symlinked stores, yielding faster warm installs. However, caution is required: symlinks spanning worktrees can cause catastrophic unintended deletions if cleanup commands traverse outside the worktree root.

`tsc --incremental`

and `eslint --cache`

.By optimizing the infrastructure pipeline, fixed job overhead drops from **5–8 minutes to under 60 seconds**. The remaining runtime represents actual model reasoning—the exact phase worth waiting for.

*I'm Andréas — full-stack dev, CTO at a B2B SaaS, building my own agent tooling. Portfolio: https://andreas-bodin.vercel.app*