# IO Harness
> A Rust agent harness that runs AI agents from a typed task contract to a checked result.
The shared engine every initorigin app (io-cli, io-studio) and io-eval build on.
**Type:** Rust library crate
**Stack:** Rust · cargo · tokio · rusqlite · rmcp · own HTTP+SSE provider client
**License:** Apache-2.0
**Status:** Pre-release. v0.1 shipped the single-agent file-edit loop (filesystem tool, OpenRouter provider, deterministic verify, rusqlite audit). v0.2 adds step/time/cost budgets, retry with escalation, a full trace, resumable runs, and execution-based verification that compiles the produced file so a substring stub cannot pass. v0.3 adds repository-wide work — `grep` and `find` tools over a workspace and multi-file edits in one run — and two more providers (Anthropic and OpenAI) behind the same provider-agnostic surface, selected at run construction. v0.4 adds the permission boundary: a layered policy over reads, writes, and command execution, enforced in the tool layer rather than the prompt, plus a human-approval gate that can approve, rewrite, remember, deny, or defer a decision until after the process has exited.
## Capabilities
- Task contract — goal, constraints, expected output, success criteria
- Context construction — feed the model only relevant, current, trusted info
- Tool layer — narrow, typed actions the agent invokes
- Orchestration loop — observe, reason, act, check, stop
- State and memory — progress, intermediate results, decisions (rusqlite)
- Verification layer — tests, schemas, read-backs confirm the task is done
- Permissions and guardrails — what the agent may access, change, send, spend
- Recovery and retry — retries, fallbacks, replanning, escalation
- Stop conditions and budgets — cap steps, time, cost, retries, risky actions
- Observability and tracing — record prompts, decisions, tool calls, cost
- Human approval layer — review before sensitive or irreversible actions
- Providers — OpenRouter first, then Anthropic and OpenAI (own HTTP+SSE client)
- Agent composition — spawn and nest many agents (100+) with shared context
- Long-running autonomous tasks — 24h+ with no user input
- Ephemeral local code-exec sandboxes — write, run, capture, destroy
- Built-in tools — filesystem, git, grep, find
- Office and document tools — Word/Excel/PowerPoint/PDF create/edit/delete, PDF watermark, PDF form fill, OCR, barcode/QR read and generate
- Media — image and video passthrough when the model supports it
- Extensibility — MCP (rmcp), plugins, skills
See [docs/CAPABILITIES.md](docs/CAPABILITIES.md) for detail and
[docs/CONTRACT.md](docs/CONTRACT.md) for the public contract.
## Usage (v0.4)
Hand the harness a task contract; it runs the loop, verifies the result, records
every step to rusqlite, and stops on success or a budget. A single-file task uses
the filesystem tool; a workspace task lets the agent `grep`/`find` across a
repository and edit several files. Pick any of three providers at construction.
Everything else in **Capabilities** is roadmap.
### 1. Add the crate
```toml
[dependencies]
io-harness = "0.3"
tokio = { version = "1", features = ["rt-multi-thread", "macros"] }
```
Upgrading from 0.2: `TaskContract::new`, `run`, `resume`, and the single-file
loop are unchanged, so existing callers keep compiling. New in 0.3:
`TaskContract::workspace`, the `grep`/`find`/`read_file` tools, the
`EachCompilesRust` / `WorkspaceTestPasses` verifications, and the `Anthropic` /
`OpenAi` providers. If you implement `Provider` yourself, note it gained a
defaulted `name()` method (override it to label your provider in the trace — no
change required to keep compiling). A 0.2 rusqlite database is migrated in place
on open (a `provider` column is added; a 0.2 binary still reads it).
### 2. Choose a provider
Each provider reads its own key + model slug from the environment; credentials
are never logged, and no default model is guessed. Selecting a provider is just
constructing a different one — the task contract does not change.
```bash
# OpenRouter
export OPENROUTER_API_KEY=sk-or-...
export OPENROUTER_MODEL=anthropic/claude-sonnet-4
# Anthropic
export ANTHROPIC_API_KEY=sk-ant-...
export ANTHROPIC_MODEL=claude-sonnet-4
# OpenAI
export OPENAI_API_KEY=sk-...
export OPENAI_MODEL=gpt-4o
```
```rust
use io_harness::{Anthropic, OpenAi, OpenRouter};
let provider = OpenRouter::from_env()?; // or:
let provider = Anthropic::from_env()?; // or:
let provider = OpenAi::from_env()?;
// ...then hand `&provider` to `run` — nothing else changes.
```
### 3. Run one file-edit task, bounded and verified by execution
```rust
use std::time::Duration;
use io_harness::{run, OpenRouter, Store, TaskContract, Verification};
#[tokio::main]
async fn main() -> io_harness::Result<()> {
let contract = TaskContract::new(
"add a `hello` function that returns 42",
"src/hello.rs",
// Execution-based: the file must compile AND pass this test. A stub
// that only contains the right substring fails the gate.
Verification::RustTestPasses {
test_src: "#[test] fn t() { assert_eq!(hello(), 42); }".into(),
},
)
.with_max_steps(8) // step budget
.with_time_budget(Duration::from_secs(120)) // time budget
.with_token_budget(200_000) // cost budget, in tokens
.with_max_retries(2); // retry transient failures
let provider = OpenRouter::from_env()?;
let store = Store::open("runs.db")?;
let result = run(&contract, &provider, &store).await?;
// Success | StepCapReached | TimeBudgetExceeded | CostBudgetExceeded
println!("{:?}", result.outcome);
Ok(())
}
```
### 4. Run a repository task: grep, find, and multi-file edits
Give the agent a workspace root instead of one file. It can `grep` file contents
(regex or substring), `find` files by name/path glob, `read_file` to inspect
what it found, and `write_file` to edit several files — all confined to the root
(a `..` or absolute path that escapes is refused). Verification spans the set:
`WorkspaceTestPasses` compiles the edited files together with a test, so the run
only succeeds when the whole set is correct.
```rust
use io_harness::{run, OpenRouter, Store, TaskContract, Verification};
let contract = TaskContract::workspace(
"Make a() + b() equal 42 by editing the two source files.",
"my-repo", // workspace root
Verification::WorkspaceTestPasses {
files: vec!["src/a.rs".into(), "src/b.rs".into()],
test_src: "#[test] fn t() { assert_eq!(a() + b(), 42); }".into(),
},
);
let result = run(&contract, &OpenRouter::from_env()?, &Store::memory()?).await?;
println!("{:?}", result.outcome);
```
The grep/find tools skip `.git`, `target`, and `node_modules`. Use
`Verification::EachCompilesRust(files)` when each edited file only needs to
compile on its own.
### Execution-based verification
Content checks (`FileContains`, `FileEquals`) confirm the file *says* the right
thing but not that it *works* — the 0.1 live run passed `FileContains("fn hello")`
by writing the literal string `fn hello`, which does not compile. v0.2 adds gates
that run the artifact:
- `Verification::CompilesRust` — passes only if the file compiles (`rustc --crate-type lib`).
- `Verification::RustTestPasses { test_src }` — appends `test_src` and passes only if the test binary passes.
Compilation runs locally in a throwaway temp dir (removed afterwards) and touches
no network.
### Trace and resume
Every step's prompt, decision, tool call, and token usage is persisted. Read the
full trace back, and resume an interrupted run under its original id instead of
restarting:
```rust
use io_harness::{resume, Store};
// After a crash or a hit budget, continue the same run from where it stopped.
let store = Store::open("runs.db")?;
let result = resume(&contract, &provider, &store, run_id).await?;
for step in store.steps(result.run_id)? {
println!("step {}: {} ({} tokens)", step.step, step.decision, step.tokens);
}
```
Or run it live end to end: `cargo run --example edit_file`.
## Permissions and approval (v0.4)
A `Policy` is a stack of named layers plus a per-action default. It is evaluated
**deny-first across the whole stack**: a deny in any layer beats an allow in any
other, so a layer can add capability but can never re-allow what a layer beneath
it denied.
```rust
use io_harness::{run_with, ApproveAll, Policy, Store, TaskContract, Verification};
let policy = Policy::default() // reads open, writes ask, secrets denied
.layer("project")
.allow_read("*")
.deny_read("secrets/*")
.deny_write("secrets/*");
let result = run_with(&contract, &provider, &store, &policy, &ApproveAll).await?;
// Why was that refused? Same function the tool layer enforces with.
let verdict = policy.explain(io_harness::Act::Write, "secrets/key.txt");
println!("{:?} by rule {:?} in layer {:?}", verdict.effect, verdict.rule, verdict.layer);
```
**The default is permissive.** A caller who passes no policy — plain `run()` —
gets no enforcement and the exact 0.3.0 behaviour. The boundary is opt-in. This
is a deliberate trade-off for backward compatibility, not an oversight.
### What asks, what is refused
`Policy::default()` sets the tiers, following the same shape Claude Code uses:
| Action | Default | Note |
| --- | --- | --- |
| Read | allow | `.env`, `*.pem`, `id_rsa`, `id_ed25519`, `*.key` denied outright |
| Write | **ask** | including overwriting a file the path rules already allow |
| Exec | ask | `rustc` and `<test-binary>` allowed, so verification works |
A **denied** action never reaches the approver — it is refused and reported to
the model as a tool result it can adapt to, and the refusal consumes a step, so
a model retrying it reaches the step cap rather than looping. Only the
**ask** tier prompts.
### The approver
```rust
use io_harness::approve::{Approver, Decision, DecisionFuture, Request};
impl Approver for MyUi {
fn decide<'a>(&'a self, request: &'a Request) -> DecisionFuture<'a> {
Box::pin(async move {
match self.ask_the_human(request).await {
Answer::Yes => Decision::approve(),
Answer::No => Decision::deny("not this one"),
Answer::NotNow => Decision::Defer, // persist and decide later
}
})
}
}
```
The trait is object-safe (`Box<dyn Approver>`) and the future may stay pending
indefinitely — the run waits rather than timing out. `Decision::Approve` can
also carry a rewritten action (`modified`) or rules to `remember` for the rest
of the run. Both are re-checked against the policy: **an approval cannot move an
action across a deny, and a remembered allow cannot override one.**
Remembered rules come back on `RunResult::remembered` for you to persist.
Built-ins: `ApproveAll`, `DenyAll`, `StdinApprover`.
### Deferring past the end of the process
```rust
match result.outcome {
RunOutcome::AwaitingApproval { request_id, .. } => {
// ...hours later, another process, same rusqlite file
let store = Store::open("runs.db")?;
io_harness::resume_with_decision(
&contract, &provider, &store, run_id, request_id,
Decision::approve(), &policy, &approver,
).await?
}
_ => result,
};
```
The pending action is persisted with the content the human was shown, so the
resumed action is exactly the one approved. The policy is re-checked on resume,
so a deny that landed while it waited still holds.
### Sharing one policy between apps
`Policy` is `serde`-serializable, so io-cli and io-studio read the same format
and neither writes its own parser. Compose layers with `merge`:
```rust
let effective = shared_base.merge(app_local);
```
The recommended convention is **user base → project layer → app overlay**, each
app keeping its own config file over a shared base. The crate composes a stack
it is handed; **it does not discover config files** — locations and precedence
are the adopting app's responsibility. Because denies are absolute across
layers, a shared base stays trustworthy no matter what an app stacks on top.
Run it live: `cargo run --example policy_run`.
## Part of initorigin
`IO Harness` is one of the [initorigin](https://github.com/initorigin) products:
| Repo | What it is |
| --- | --- |
| [io-harness](https://github.com/initorigin/io-harness) | The Rust agent harness (the center product) |
| [io-eval](https://github.com/initorigin/io-eval) | Benchmark harness for io-harness |
| [io-cli](https://github.com/initorigin/io-cli) | Terminal app on io-harness |
| [io-studio](https://github.com/initorigin/io-studio) | Desktop coding studio on io-harness |
| [website](https://github.com/initorigin/website) | Marketing site, docs, and blog |
## Contributing
Read [CONTRIBUTING.md](CONTRIBUTING.md). Work branches from `develop`, lands via
PR, and every user-facing change updates [CHANGELOG.md](CHANGELOG.md). Releases
follow [docs/RELEASE_PROCESS.md](docs/RELEASE_PROCESS.md).
## Security
Report vulnerabilities per [SECURITY.md](SECURITY.md).
## License
Apache-2.0. Copyright 2026 Aakash Pawar (InitOrigin). See [LICENSE](LICENSE) and
[NOTICE](NOTICE).