Adding a distiller

The most common change here. Five steps, and the fourth is the one that matters.

1. The module

src/distillers/my_type.rs:

use crate::pipeline::{OutputSegment, SessionState};
use super::Distiller;

pub struct MyDistiller;

impl Distiller for MyDistiller {
    fn distill(
        &self,
        segments: &[OutputSegment],
        input: &str,
        session: Option<&SessionState>,
    ) -> Option<String> {
        // Return None the moment you are not sure you parsed this.
        todo!()
    }
}

Return None whenever parsing failed. That hands back the raw bytes, which is the correct answer and the one the whole design rests on.

Never return a success string from a zero state. vitest: ✓ 0/0 passed for output that was actually a dev server is failing closed, confidently, and it is the exact defect this project keeps fixing.

2. Register it

src/distillers/mod.rs:

pub mod my_type;

// in get_distiller():
ContentType::MyType => Box::new(my_type::MyDistiller),

Routing belongs in pipeline/registry.rs. Do not add a matches!(cmd, ...) block inside the distiller; that duplication is what the registry exists to prevent.

3. A realistic fixture

tests/fixtures/my_type_example.txt. Real output from the real tool, not something hand-written to be easy to parse.

4. A snapshot test, and prove it can fail

snapshot_test!(test_my_type_distillation, "my_type_example.txt", ContentType::MyType);

cargo test
cargo insta review

Then break the rule deliberately and watch the test go red, before restoring it. A check that cannot fail proves nothing, and this repo has shipped two regression tests that could not fail.

Two specific ways a test here passes for the wrong reason:

• Your fixture reaches a different collapse mode than you think. A kubectl … | grep fixture exercises Infra, not Log, so a guard you are testing may never be consulted.
• “No rewrite from the hook” is not proof the distiller punted. It can mean the format gate fired, or the guardrail rejected the result.

A distiller can also return a near-copy rather than the exact input, so detect “this did not help” with beats_guardrail rather than comparing against the input.

5. Gates

cargo fmt
cargo clippy -- -D warnings
OMNI_DB_PATH=/tmp/t.db cargo test

OMNI_DB_PATH is not optional. Parallel tests competing for ~/.omni/omni.db cause SQLite locks: 79 seconds green against an isolated database, 433 seconds and then a hang against the live one.

Before you write any of it

Measure the workload. ~/.omni/omni.db prices a proposal in one query, and the answer is often the opposite of the request.

“Improve the python3 distiller” turned into two facts in two queries: python3 was already reporting 97.2%, and the savings were the collapse fallback deleting data rows. The obvious feature, a traceback distiller, died on 9 of 7,506 traces containing a traceback.

-- distillations.filter_name is the command's first token
-- execution_traces holds raw_input and distilled_output in full

Read the rows before quoting an aggregate over them. A LIKE filter that caught the wrong rows has already put a wrong figure into a published issue.

And never read sqlite3 output through the Bash hook while doing this. The pipeline can fold the rows you are counting.

The bar the result has to clear

Not “did it compress”. These:

1. Would the agent still have the answer?
2. Does anything dropped leave a marker?
3. Does the reported number describe what actually happened?

A patch that raises reduction percentage while removing signal is the project’s own recurring defect, shipped again with your name on it.