App startup and bootstrap Agent Skill

Enforces a fixed main() cold-launch order — crash-log sink + FlutterError.onError + PlatformDispatcher.onError installed BEFORE any code…

Context cost
4.1k tokensestimated from the bundle, loaded when it triggers
Bundle
1 file · 16.3 kBtext throughout, nothing executable
Licence
MITthe author’s own terms
Last change
—no release on file
Servers it uses
Noneruns standalone

What it does

Enforces a fixed main() cold-launch order — crash-log sink + FlutterError.onError + PlatformDispatcher.onError installed BEFORE any code that can throw, settings/theme read before runApp so the first frame paints correct, real infra constructed in a composition-root bootstrap() and injected via ProviderScope overrideWithValue over throwing placeholder providers, non-blocking warm-up deferred to addPostFrameCallback, exactly two error handlers with NO runZonedGuarded, ProviderException unwrapped before logging, and a WidgetsBindingObserver that flushes durable state on background/resume.

What this skill changes about the agent has not been set out here as a list. Its SKILL.md, shown below, says it in the author’s own words.

mobile

The skill itself

A skill is instructions the model reads, so you can see what you are getting: below is the start of its SKILL.md. The front matter loads with every session, the body loads when the skill triggers, and the whole file comes with the install.

SKILL.md16.3 kB · preview
--- name: app-startup-and-bootstrap ---
6# App startup and bootstrap
7
8main() has one job: install a crash net, read the little state the first frame needs, wire real dependencies into the tree, and hand off to runApp — fast, ordered, and unable to hide a failure. Everything expensive happens after the first frame or off the launch path entirely.
9
10## Non-negotiable rules
11
121. **Error handlers go first, before anything that can throw.** A crash-log sink, FlutterError.onError, and PlatformDispatcher.instance.onError are installed immediately after WidgetsFlutterBinding.ensureInitialized(). The step most likely to throw is opening the DB; installing handlers after it inverts the whole point.
132. **Exactly two error handlers — no zone.** FlutterError.onError (build/layout/paint errors) and PlatformDispatcher.instance.onError (uncaught async errors) cover every path. **Never add runZonedGuarded.** The "you need all three" advice is crash-SDK advice (Sentry wraps its init in a zone); with no such SDK a zone buys nothing and costs a documented zone-mismatch footgun. Flutter's own fix for that warning is to remove zones.
143. **PlatformDispatcher.onError returns true unconditionally.** Returning false routes to the embedder fallback, where the process may exit or hang. Get debug-console visibility from debugPrint under kDebugMode, not from return kReleaseMode.
154. **Never let an error handler throw.** Wrap its body in a bare try/catch (_) and keep the comment explaining why the discarded error is deliberate — otherwise someone "fixes" it into infinite recursion inside the handler.
165. **Read settings/theme before runApp.** Palette, text-scale policy, locale, and any first-paint choice are read synchronously (a handful of rows is sub-10ms) so frame one paints correct. A flash of the wrong theme is a visible defect, not a cosmetic one.
176. **Construct real infra in a composition-root bootstrap(), inject via overrides.** Feature code depends on **throwing placeholder providers**; bootstrap() builds the real DB/services and overrideWithValues them in the root ProviderScope. A forgotten wiring fails loudly at startup, never returns null. This is also the test seam.
187. **Defer warm-up to addPostFrameCallback; never await it in main().** Any plugin/engine warm-up (audio, TTS, first network handshake) runs its cost synchronously on the main thread and produces ANRs on the cold-start path. Fire it best-effort after the first usable frame.
198. **Do not block the first frame.** The only launch-path await is the one unavoidable blocker (opening the DB). Show the UI shell immediately rather than a blank window while a migration runs.
209. **Unwrap ProviderException before logging.** Riverpod 3 rethrows provider failures wrapped; logging the wrapper hides the real cause and makes every entry read ProviderException.
2110. **Tune Riverpod retry for the app's failure model.** Riverpod 3 retries failing providers by default (~38s of exponential backoff). For a provider whose only failure is a local bug (corrupt DB, missing file), set retry: (count, error) => null so it fails immediately and loudly instead of spinning behind a spinner.
2211. **Flush durable state on background via one lifecycle observer.** Register a single WidgetsBindingObserver and, in didChangeAppLifecycleState, flush pending writes when the app reaches inactive/paused — the OS can kill a backgrounded app with no further callback — and re-read time-sensitive state on resumed. This is bootstrap's mirror image: bootstrap() restores state on cold launch, the observer persists it before the process can die. Read services in the callback via ref.read (never watch).
23
24## The sequence
This is a preview of SKILL.md. Download or install the skill to get the whole thing.
In the file
SKILL.md2,051 words
Files1
LicenceMIT
Why you can read it

Nothing in a skill executes. The client loads the text and the model follows it, so a skill can be audited the way a runbook is — by reading it.

What it costs in context

Skills are not billed by the call. They are paid for in context: every token the instructions occupy is a token your code, your diff and your conversation cannot use. Here is what this one takes and when it takes it.

≈250
always loaded
The name and description, so the model knows the skill exists and when to reach for it.
3,825
on trigger
The instruction body, read only when the skill fires.
2.0%
of a 200k window
Ten skills this size would take about 20% of the window before you open a file.
050k100k150k200k context window

4.1k tokens, estimated from the bundle at four bytes to the token, held for the rest of the session once it triggers. Heavy. Teams tend to install this one per project rather than globally, and load it only when the job comes up.

Servers bill, skills cost

A server charges by the month. A skill charges once per session, in context, and then keeps charging it for as long as the session lives.

Before and after

The same question, put to the same model twice: once as it comes, and once with these instructions loaded.

No worked example has been published for this skill yet.

The procedure it runs

The procedure has not been set out here step by step. It is in the body of its SKILL.md: the start of it is shown above, and the whole file comes with the install.

Prose, not code

These steps are written for a model to follow, not executed by a runtime. It can still be told to skip one, and it will say so when it does.

Servers it uses

None. This skill calls no MCP servers at all.

Everything it needs is in the instructions, so it works in a project with nothing connected — the model reads the file and changes how it works with what it can already reach.

Its SKILL.md does not declare which tools it asks the agent for, so what it touches is whatever the instructions themselves ask for — read them before you install it.

What it asks for
Writes filesnot declared
Network accessnot declared

This SKILL.md carries no allowed-tools line, so neither is declared. A skill grants no permissions of its own — it can only ask for tools your client already has.

What it will not do

Every skill is narrow, and the useful ones say where they stop. These are the jobs this one is the wrong tool for.

What this skill is not for has not been published here. Nothing is implied by that: it is a section the author has not filled in.

What is in the bundle

1 file, 16.3 kB on disk. A bundle is text throughout: the instructions the model reads, plus the templates it fills in.

  • SKILL.md16.3 kB
What is not in it

No dependencies and nothing executable: a skill is text the agent reads, so the bundle is 1 file you can review in full before installing. The MIT licence covers the templates and examples as well as the instructions.

Install

Installing copies the bundle into your project. Nothing runs at install time — the files sit on disk until the model reads them.

# App startup and bootstrap · 4.1k tokens when loaded · macOS, Linux mkdir -p .claude/skills && t=$(mktemp -d) && curl -fsSL -o "$t/bundle.tar.gz" https://mcprush.com/api/skills/app-startup-and-bootstrap/bundle.tar.gz && tar -xzf "$t/bundle.tar.gz" -C "$t" && [ -d "$t/app-startup-and-bootstrap" ] && { [ ! -e .claude/skills/app-startup-and-bootstrap ] || { mv .claude/skills/app-startup-and-bootstrap "$t/.previous" && echo "Previous copy moved to $t/.previous"; }; } && mv "$t/app-startup-and-bootstrap" .claude/skills/ && echo "Installed .claude/skills/app-startup-and-bootstrap"
On Windows, or any OS with Node 20+
npx mcprush@latest skill add zakariaf/app-startup-and-bootstrap

Windows PowerShell says 'running scripts is disabled on this system'? Run Set-ExecutionPolicy -Scope CurrentUser RemoteSigned once, or type npx.cmd instead of npx (codex.cmd, gemini.cmd, grok.cmd likewise). PowerShell 7 needs neither. Writes to .claude/skills/app-startup-and-bootstrap/ in the current project. For every project instead, run mkdir -p ~/.claude/skills && t=$(mktemp -d) && curl -fsSL -o "$t/bundle.tar.gz" https://mcprush.com/api/skills/app-startup-and-bootstrap/bundle.tar.gz && tar -xzf "$t/bundle.tar.gz" -C "$t" && [ -d "$t/app-startup-and-bootstrap" ] && { [ ! -e ~/.claude/skills/app-startup-and-bootstrap ] || { mv ~/.claude/skills/app-startup-and-bootstrap "$t/.previous" && echo "Previous copy moved to $t/.previous"; }; } && mv "$t/app-startup-and-bootstrap" ~/.claude/skills/ && echo "Installed ~/.claude/skills/app-startup-and-bootstrap" (macOS, Linux) — or add --global to the npx line. The curl line replaces .claude/skills/app-startup-and-bootstrap/ only after the download succeeds, so files left there by another skill of the same name, or by an older release, do not mix in. A copy already there is moved aside, not deleted, and the line prints where.

Which clients pick it up on their own

A skill is a folder of text. Most of these read a skills folder and pick it up without being told; the rest take the same folder another way — an upload in the app, a parameter on an API call — and then choose it by its description just the same.

Claude Code.claude/skills/
Claude DesktopCustomize › Skills
ChatGPTSkills › Create › Upload
Cursor.cursor/skills/
VS Code.github/skills/
Codex CLI.agents/skills/
Gemini CLI.gemini/skills/
Grok Build.grok/skills/
Microsoft CopilotSkills › Upload a skill
PerplexityComputer › Skills › Upload a skill
DeepSeek Harness.dsh/skills/
Zed.agents/skills/
Devin Desktop.devin/skills/
Windsurf (legacy).windsurf/skills/
OpenAI Agents SDKInstructions or sandbox Skills
HTTP / APIa request parameter
This release
Versionnot versioned
Publishedno release date on file
PriceFree
Referencezakariaf/app-startup-and-bootstrap

Versions

Its author publishes no version number, so there is nothing here to pin to: what you install is the folder as it stands today. Instructions change more often than APIs do — a skill can be rewritten entirely without anything it depends on moving.

Pinning

Nothing to pin to: this skill carries no version number of its own. What you install is what the folder holds on the day you install it.

Reviews

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