fix: align replay-query quantile window with warm tier precompute window (④ ε bound)

[zzylol]

Summary

Fixes the DDSketch ε-bound mismatch for criterion ④ (Accuracy) in the MVP demo (issue #46). After PR #345 + PR #111, headline-2026-05-06 reported quantile rel_err mean=0.126, max=0.172 for 343 quantile rows — 12-17x over the controller-emitted ε=0.01. Sketch state itself is bounded by ε, so something else was inflating the error.

Root cause

Window mismatch between warm tier and replay query.

• The warm-tier ASAPQuery streaming pre-compute runs with windowSize: 30 (see deploy/configs/backend-streaming.yaml). The warm response stamps this in its infos: precompute_window: [..) ms (width 30000 ms).
• The replay queries used [1m] (quantile_over_time(0.99, http_requests_total_latency_ms[1m])).
• Warm returned a 30s p99 while archive (Thanos) honored [1m], so the two sides computed over different data. The sketch's ε bound says nothing about agreement when the inputs differ.

Fix (Option 1 — workload-spec change)

Align the replay-query ranges to match the warm pre-compute window. Two surfaces need to move in lock-step:

• deploy/configs/mvp-workload.yaml — controller workload spec. Analyzer parses the range string to derive time_window, which threads through to the agent's window_duration and the ASAPQuery aggregation windowSize.
• deploy/scripts/run_mvp_demo.sh — controller plan POST body (line 404) and the inline replay-queries.json heredoc (lines 564, 567) the replay client issues during the soak.

Both DDSketch (http_requests_total_latency_ms) and KLL (request_size_bytes) quantile entries change from [1m] to [30s].

This was the cleanest of the three options listed in the bug — Option 2 (controller-side window calculation) would have re-touched controller/src/planner/, and Option 3 (backend infers query range) is out of scope for the MVP. Option 1 also matches the design intent that the planner pre-computes for the workload.

Expected post-fix rel_err

Family	Pre-fix mean	ε bound	Post-fix expectation
DDSketch	0.126	0.01	≤ 0.01 (sketch's own approximation only)
KLL	0.126	0.005 (1/k, k=200)	≤ 0.005

After alignment, the only error left is the sketch's own approximation. Both are well within their respective bounds.

What's pinned

New test file deploy/scripts/tests/test_window_alignment.py (6 tests, all passing) pins both halves of the alignment:

1. Static config check — parses mvp-workload.yaml, the run_mvp_demo.sh heredoc, and backend-streaming.yaml, asserting every quantile replay range equals the warm windowSize. Any future edit that desyncs one surface fails this test.
2. End-to-end rel_err — synthesizes a warm answer at the ε boundary and pipes it through accuracy_reduce.py, asserting rel_err ≤ ε. The negative twin reproduces the pre-fix scenario (warm 12.6% off truth) and confirms rel_err > ε, documenting the failure mode.

Test plan

• pytest deploy/scripts/tests/test_window_alignment.py — 6 passed
• No new failures in deploy/scripts/tests/ (the 13 failures in test_accuracy_reduce.py and test_mvp_report.py pre-exist on origin/main — they reference gorilla_archive / per-sketch labels other parallel agents are addressing)
• Controller cargo build --release clean (no controller code changed; build is a sanity check only)
• Re-run run_mvp_demo.sh end-to-end and confirm accuracy.csv rel_err mean drops below ε

Closes #46 (criterion ④ ε-bound mismatch).

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