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* feat(query): implement PromQL @ modifier on vector and matrix selectors The planner previously dropped the `at` field of selectors (`at: _`), so `some_metric @ 300` silently returned step-following values instead of the samples anchored at the fixed timestamp. Anchoring follows Prometheus's `setOffsetForAtModifier` + `refetch` semantics: resolve the anchor (`@ <ts>`, `@ start()`, `@ end()`), apply `offset` to the anchor, rewrite the selector offset to `eval_start - anchor`, scan only the anchored window, then report the same window at every evaluation step via a grid-wide-replay `InstantManipulate`. `@ start()` / `@ end()` resolve against the statement's evaluation range (`stmt_start` / `stmt_end`), which subquery planning does not rewrite. Timestamps before the Unix epoch are accepted; unrepresentable ones are rejected with `AtModifierTimestampOutOfRange` instead of wrapping. Selectors without `@` are planned exactly as before. Report: .e-agent/greptimedb_promql_compatibility_report_2026-09-16.md P0-2 Signed-off-by: discord9 <55937128+discord9@users.noreply.github.com> * fix(promql): center predict_linear on the evaluation timestamp predict_linear_impl used the window's last sample time as the evaluation timestamp, and the UDF took only (ts_range, value_range, t) with no channel for the current instant. After a range selector is folded for @ (or with an offset) the same window is replayed at every step, so the prediction stayed constant at the anchor's answer; even a plain window ended before the step produced a stale value. Give prom_predict_linear a 4th argument carrying the step's evaluation instant (ms timestamp), derived in the planner from the row's time index plus the offset the window was folded with (at_offset for @, offset_ms otherwise, recorded on PromPlannerContext). The regression is centered on that instant, matching Prometheus' use of enh.Ts. The mixed float/native-histogram path forwards the same argument. Signed-off-by: discord9 <55937128+discord9@users.noreply.github.com> * refactor(query): tighten @ modifier planner and predict_linear - range_fold_offset is always a concrete millisecond offset, not an Option; the single-step replay helper no longer wraps an infallible plan in Result. - predict_linear's eval timestamp is always cast to Timestamp(ms) at the call site, so the UDF drops its dead Int64 branch and the extra func_name argument. - Drop two redundant comparison cases from the at_modifier sqlness test and fix the lookback window comment to the half-open (0s, 300s]. Signed-off-by: discord9 <55937128+discord9@users.noreply.github.com> * test(query): accept parse-time rejection of @ on Windows `@ 1e16` is 10^19 milliseconds, beyond i64::MAX. A Unix SystemTime holds it and the planner rejects the anchor it cannot represent, but a Windows SystemTime tops out near 1.8e12 seconds, so the parser's checked_add fails first and the same literal is rejected while parsing. Accept either rejection path so the test passes on both platforms. Signed-off-by: discord9 <55937128+discord9@users.noreply.github.com> * fix(query): avoid replaying label_join over rewritten series keys Signed-off-by: discord9 <55937128+discord9@users.noreply.github.com> * fix(query): narrow anchored range call promotion Signed-off-by: discord9 <55937128+discord9@users.noreply.github.com> * fix(query): address @ modifier review feedback Signed-off-by: discord9 <55937128+discord9@users.noreply.github.com> * fix(query): satisfy super import format check Signed-off-by: discord9 <55937128+discord9@users.noreply.github.com> * docs(query): address at modifier review follow-ups Signed-off-by: discord9 <55937128+discord9@users.noreply.github.com> --------- Signed-off-by: discord9 <55937128+discord9@users.noreply.github.com>