# 005 — FilterBar query language (pest grammar)

## Summary

Build the syntax-aware search language described in the README's FilterBar section,
using `pest`, supporting regex searches and metric comparisons combined with
boolean operators.

## Scope

- Add `pest` + `pest_derive` dependencies.
- Grammar covering:
  - `regex("...")` — raw-text regex search over log lines.
  - `metric_name[param] <op> value` comparisons (`<`, `>`, `<=`, `>=`, `==`, `!=`) —
    `metric_name[param]<5` per the README example.
  - `sequence` and `timestamp` as reserved metric names usable the same way
    (`sequence<5`, `timestamp>12:00`).
  - Boolean combinators `and` / `or` with standard precedence, e.g.
    `regex("error") and sequence<5 or timestamp>12:00`.
- Parse into an AST (not directly into engine queries — that's
  [007](007-filterbar-integration.md)).
- Surface parse errors with position info suitable for showing under the FilterBar
  input.

## Acceptance criteria

- Grammar test cases cover: bare regex, single metric comparison, reserved-metric
  comparison, `and`/`or` combinations with correct precedence, and at least one
  malformed-input case producing a located error rather than a panic.
- Parser is a standalone module with no dependency on the engine/index types, so it
  can be unit tested in isolation.

## Depends on

None directly, but the metric-comparison side of the grammar is only meaningful once
[002](002-metric-declarations.md) exists — build/test this ticket against metric
names as opaque strings.