[M0-CORE-08] Budget harness: Histogram/TimeIt/budgetCheck + budgets.json + laige-bench - #9
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…son + laige-bench laige::Histogram: fixed-capacity rolling window; O(1) allocation-free record(); exact min/mean/p50/p95/p99/max over the stored window with nearest-rank percentiles (rank = ceil(p*n/100), exact integer math); stats() is a cold-path O(n log n) pass with no allocation (pre-allocated scratch). laige::TimeIt: steady_clock ms scope timer, no allocation. loadBudgets: file I/O + bounded parse (ADR 0003) + strict budgets.json schema v1 validation (ARCH-007; unsupported version/fields, bad name/metric/unit charset, duplicate names, negative or non-finite numbers -> MalformedInput; unreadable file -> IoError). budgetCheck: total operation; empty histogram -> loud NO_SAMPLES; target > 0 -> measured <= target; target == 0 -> hard-zero budget (sim_heap_allocs), not "not set" (the not-yet-measured marker is the initial measured: 0). Report = stable 4-line AGENTS §12 text with before/after pair and caller context; formatStatsLine is the single source of the stats text. budgets.json (repo root): all 15 PRD §8.1 budgets as named entries; measured: 0 = not yet measured until their subsystems land (M1+). laige-bench: canonical command ./build/bin/laige-bench --suite=<name> (reserved for this step by docs/getting-started/building.md); M0 suite "synthetic" (deterministic, allocation-free 4096-step LCG + double stand-in workload); --runs/--warmup, --budget=<name> check with --budgets path resolution (arg -> LAIGE_BUDGETS_PATH env -> budgets.json), --report append; exit 0 pass / 1 usage or load failure / 2 budget check failure (CI-gateable). ctest: budget_harness entry (22 GTest cases) + laige_bench_smoke entry; LAIGE_BUDGETS_PATH wired for both (incl. the TSan tree, where CTest ENVIRONMENT is last-write-wins). API contract: docs/api/budget_harness.md. Bug fix (M0-CORE-07) found by the Verify run of this step: json.cpp parseObjectMembers was missing skipWhitespace before the member key - object documents with ", " between members (the hand-formatted repo-root budgets.json) were rejected. Regression test ConfigJsonValid.ObjectMemberWhitespace fails pre-fix. Verified locally: ctest 16/16, zero warnings, on GCC 16.2.1 (static, shared, ASan+UBSan fatal, TSan halt_on_error=1) and Clang 22.1.8 trees; include-lint clean (17 files). MSVC/AppleClang compile proof lands in CI.
M0-foundations.md: M0-CORE-08 checked, with Decision (2026-09-11), Verify (22 GTest cases + laige_bench_smoke; 16/16 ctest on GCC static, shared, ASan, TSan and Clang trees) and Size notes, including the record of the M0-CORE-07 parser bug fix found by this step's Verify run (missing skipWhitespace before the object member key). README.md: Progress Board M0 11 -> 17 (Total 17), and the change log gains this step's line (810c251) plus the five reconstructed lines for M0-CORE-03..07 (0fd41f3, 5c76991+7538053, 4a572af+ba4ffb2, a82de8e, 41938b0) rebuilt from their step records in M0-foundations.md — the board and change log had drifted (11 vs 16 checked boxes) since M0-CORE-03 landed.
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Scope (M0-CORE-08, per
roadmap/M0-foundations.md):laige::Histogram— fixed-capacity rolling window; O(1) allocation-freerecord(); exact min/mean/p50/p95/p99/max over the stored window via nearest-rank percentiles (rank = ceil(p·n/100), exact integer math); allocation-freestats().laige::TimeIt—steady_clockms scope timer.loadBudgets/budgetCheck— strictbudgets.jsonschema v1 (ARCH-007) over the M0-CORE-07 bounded JSON parser (no new dependencies); AGENTS §12 report: stable 4-line machine-greppable text with before/after pair and caller context;formatStatsLineis the single source of the stats text.budgets.json(repo root) — all 15 PRD §8.1 budgets as named entries;measured: 0= not yet measured until their subsystems land (M1+).laige-bench— the canonical command./build/bin/laige-bench --suite=<name>reserved bydocs/getting-started/building.mdfor this step; M0 suitesynthetic(deterministic, allocation-free stand-in workload);--budget=<name>check with exit code 2 on failure (CI-gateable per PRD §8.1).docs/api/budget_harness.md.Key design decisions:
target == 0is a hard-zero budget (e.g.sim_heap_allocs: zero steady-state heap allocations per frame), not "not set" — the not-yet-measured marker lives inmeasuredonly. An empty histogram is a loudNO_SAMPLESfailure (no silent pass — CORE-008). The 1 MiB bound is enforced before the read; unreadable file →IoError, every schema violation →MalformedInput(no new error codes).Bug fix (M0-CORE-07) found by this step's Verify run:
json.cppparseObjectMemberswas missingskipWhitespacebefore the member key — object documents with", "between members (the hand-formatted repo-rootbudgets.json) were rejected. Fixed with a regression test (ConfigJsonValid.ObjectMemberWhitespace, fails pre-fix); the documented grammar was already correct, the implementation did not match it.Verify (local, 2026-09-11):
ctest16/16, zero warnings under the NFR-8.10 policy, on five Linux trees — GCC 16.2.1 (buildstatic,build-shared,build-asanASan+UBSan fatal,build-tsanTSanhalt_on_error=1) + Clang 22.1.8 (build-clang).budget_harnessCTest entry = 22 GTest cases: known percentiles on 1..100, full-ring wrap dropping the oldest, empty → NaN, loud FAIL when a threshold is exceeded, hard-zero-target budget, 13-case schema-rejection corpus against the repobudgets.json,IoErroron missing file. The synthetic workload producing percentiles is exercised end-to-end by thelaige_bench_smokeentry.include-lintclean (17 files). The MSVC + AppleClang compile proof lands in this PR's CI run (default Linux lane).Also in this PR (roadmap bookkeeping, per the roadmap agent contract):
roadmap/M0-foundations.mdM0-CORE-08 checked with Decision/Verify/Size;roadmap/README.mdProgress Board M0 11 → 17 (Total 17) and the change log gains this step's line plus five reconstructed lines for M0-CORE-03…07 — the board and change log had drifted (11 vs 16 checked boxes) since M0-CORE-03 landed, so they are brought back in sync in the same PR that checks the next box.