# 044 — Add `ottyl_fmt` reserved param; rename `sequence`/`timestamp` to `ottyl_seq`/`ottyl_ts`

## Summary

`sequence` and `timestamp` are handled as reserved query metric names in the
filter grammar (`src/filter_parser.rs`, e.g. `parses_reserved_metric_sequence`,
`parses_reserved_metric_timestamp_as_raw_value`) and in alert evaluation
(`src/alerts.rs:199,208`, restricted per the comment at `src/alerts.rs:3` to
`regex/sequence/timestamp/json[field]`), backed by `LogLine { sequence,
timestamp_ms }` in `src/dto.rs:11-12`. These names collide with ordinary
user-declared params and don't signal that they're ottyl-owned. Separately,
there is currently no reserved param exposing which format
(`auto_declare_params`/`auto_derived`, `src/engine.rs` and `src/logfmt.rs`,
added in "Auto derived format") was used to parse a given log line — that
information is computed but not surfaced as a queryable/orderable param.

## Scope

- Add a new reserved param `ottyl_fmt`: a text-enum value recording which
  format a line was derived with (e.g. auto-detected key=value/logfmt vs.
  JSON vs. plain/none), populated wherever `auto_declare_params`/format
  detection currently runs (`src/engine.rs`, `src/logfmt.rs`).
- Rename the reserved metric names `sequence` → `ottyl_seq` and
  `timestamp` → `ottyl_ts` everywhere they're recognized: filter grammar
  (`src/filter_parser.rs`), alert query restriction and evaluation
  (`src/alerts.rs`), and any webapp references to these literal names
  (`webapp/src/lib/api.ts`, `webapp/src/components/LogPreview.tsx`).
- Decide and implement backward compatibility: either accept both old and
  new names for one release, or treat this as a breaking rename (update
  fixtures/docs accordingly) — call this out explicitly in the PR.
- Update any docs/help text (e.g. regex cheat sheet, param declaration UI)
  that reference `sequence`/`timestamp` by name.

## Acceptance criteria

- Filters, alert queries, and metric declarations recognize `ottyl_seq`
  and `ottyl_ts`; the old bare names either error clearly or continue to
  work per the compatibility decision above, but are no longer the
  documented names.
- `ottyl_fmt` is queryable/filterable like other reserved params and its
  value reflects the actual detected format for a given log line
  (verified by a seeded fixture with mixed-format lines).
- Existing tests referencing `sequence`/`timestamp` reserved metrics are
  updated and pass.

## Depends on

None.