Separate execution placement from logical semantics and cost ingestion-time alternatives #530

Execution at ingestion time or query time should be a physical planning choice based on cost and runtime capabilities, not an intrinsic restriction on a logical computation. This is a concrete follow-up to #528 and complements #520; the intended representation follows #511.

Problem

The merge/scalar migration in #528 (commit 477decd) preserves current execution correctness by restricting maintenance arithmetic. In crates/types/src/ir/timing.rs, forces_query_time and ingestion-time binary validation use per_series_rows to require matching series populations. In crates/asap-aware-mapping/src/summary_maintenance_lifecycle.rs, lifecycle enumeration disables retained alternatives when that validation fails.

For example:

sum(sum_over_time(m[1m]) + sum_over_time(n[1m]))

The current AlignedBinary implementation requires identical key sets, so it cannot implement general matching between different selectors. This is a limitation of that physical implementation, not proof that the computation must run at query time. An ingestion-time implementation could maintain both operands, match labels, process updates/removals, and recompute affected results; its state and update cost may be high.

Requested change

• Preserve logical semantics independently of execution placement. Treat every computation as eligible in principle for either placement, with any required evaluation context and dependencies represented explicitly.
• Enumerate ingestion-time and query-time physical alternatives. Include incremental maintenance or recomputation where supported, and account for state, matching, update propagation, recomputation, and query-read costs.
• Keep the identical-key requirement on AlignedBinary itself. Use a general matching implementation for different populations, or report that physical alternative as unsupported by the current runtime. Do not turn missing implementation support into a logical query-time-only restriction.
• Replace the logical timing/lifecycle exclusions introduced in refactor: unify logical operators and scalar expressions #528 with physical capability checks and cost-based selection. Retain correctness guards until an appropriate implementation exists; simply deleting validation is not sufficient.
• Coordinate with Move execution timing out of the logical DAG, then rename PostAsapDag — after #511 #520 so moving timing metadata also removes timing-dependent changes in operator meaning. This issue focuses on placement eligibility and physical alternatives, rather than DAG renaming.

Acceptance criteria

• The example above retains the same logical meaning at either placement. With both physical implementations available, changing workload/update/read costs can change the selected placement.
• Both implementations agree for disjoint and overlapping label sets, empty inputs, updates, removals/staleness, and window movement. Preserve the existing regression tests maintained_arithmetic_over_different_selectors_matches_prometheus and maintained_arithmetic_over_one_selector_executes.
• Unsupported ingestion-time execution is reported as a physical capability gap, without silently using AlignedBinary or declaring the logical computation query-time-only.
• Placement changes preserve matching, scalar/vector, and empty-result semantics; they do not change which computation the graph represents.