room-share: a legacy room's read recomputes the clamp target per line, so a long log reads in quadratic time - #2788

Fixes #2766

Owner: Dev-1
Written-by: Dev-1
Bot: Dev-1
Reviewer: Birfy
Claim-Id: cf0f9c9d48a042a1a6a760635f30b2c3
Base: bd583bd
Risk tier: T3

What changed

linesFrom (core/src/host/room-membership.js) asked floorOf(room, actor) once per line, inside the filter predicate. floorOf calls clampTargetOf, and for a room saved before rooms carried a seq counter that is a reduce over the whole log — so reading an n-line legacy room reduced n times over n lines and the read was quadratic (20,000 lines ≈ 28 s in the test below).

After: linesFrom resolves the floor once, then filters with that number. The membership window, the clamp to room.seq (or to the log's last seq for a room without one), the per-room/reader memo from #2754, and the one-time warning are all unchanged; only the number of times the floor is computed per read changes, from n to 1. Both read entry points (rt.linesVisibleTo and rt.roomHistory) go through linesFrom, so both are covered by one change.

core/test/room-floor-once.test.js counts the reduces instead of timing them: a legacy room at 20,000 lines must reduce once per read (linesVisibleTo and roomHistory), a room that has a counter must reduce zero times, the visible line count stays 20,000 and a healthy room stays silent.

Verification at the tip

Tip SHA: 613cca3
Tree: 84e9cc56e4ba051bfbaa00cd6bdf630cf52ed802 — the tree of the local commit 7265b5779e8941073d476127b048220fe56a3984 (parent bd583bd0e89989b9f31420619a22864d706ecb09). .flybot_push.py re-created the head on live main, so the pushed tip names the PR and carries exactly this tree; nothing in it was regenerated after the push.

Red first, on the base the branch starts from (bd583bd0)

The tree carried only core/test/room-floor-once.test.js; the source was untouched.

• node --test core/test/room-floor-once.test.js → # tests 3 / # pass 1 / # fail 2
• not ok 1 - a legacy room read computes its clamp target once, not once per line → the clamp target is computed once per read, saw 20000 (# legacy linesVisibleTo n=20000: 28852ms, reduce calls=20000)
• not ok 2 - a legacy room history read computes its clamp target once too → the same sentence (# legacy roomHistory n=20000: 28345ms, reduce calls=20000)
• modern control: # modern linesVisibleTo n=20000: 12ms, reduce calls=0

After the fix

• node --test core/test/room-floor-once.test.js core/test/room-membership.test.js core/test/room-context.test.js → # tests 50 / # pass 50 / # fail 0 (3 new + 47 existing), legacy linesVisibleTo 7ms / roomHistory 7ms, reduce calls=1, modern 4ms, reduce calls=0

Patches and docs

• node scripts/ds-bot-patches.mjs generate rewrote patches/ds-bot/files/ (390 files) and all ten patch series files; the committed result differs from bd583bd0 in exactly two generated paths: patches/ds-bot/files/src/host/room-membership.js and the new patches/ds-bot/files/test/room-floor-once.test.js. patches/ds-bot/0012-room-membership.patch is byte-identical to the base (it carries upstream-file edits only; a files/ mirror is not part of it).
• node scripts/ds-bot-patches.mjs check → ok ds-bot/ = Fei2411/DeepSeek-Bot@2b10c70 (tree 5834c00, v0.1.5), ok 10 patches apply cleanly in order, ok core/ equals ds-bot/ + patches/ds-bot/
• node scripts/ds-bot-patches.mjs canonical → ok patches/ds-bot/ is what generate writes (generate is a no-op)
• ARCH_DOCS_BASE=bd583bd0e89989b9f31420619a22864d706ecb09 npm --prefix core run arch-docs → arch-docs: OK (6 changed file(s))
• node .github/scripts/changelog.mjs check → changelog: 18 fragment(s) in changelog.d/ are well formed

Full suite

TZ=UTC npm run verify → exit 0.

• core # tests 3185 / # pass 3185 / # fail 0
• social 619/619, tree 143/143, timeline 161/161, workflow 516/516
• .github/scripts + policy 671/671
• interop 37/37, live-e2e 34/34

Ran with DSH_HARNESS=/home/xuke/work/dev-5/core/dev/harness (a DeepSeek Harness install carrying @deepseek-ai/*, jsdom 29.1.1 and oxlint 1.76.0, which is what npm run harness installs), and with a PATH that has no pnpm on it: this box has /usr/bin/pnpm and /bin/pnpm, and the two core/test/bench-preflight.test.js cases build a PATH deliberately devoid of pnpm, so on this host the unmodified test fails on main too. Under a PATH of the same tools minus pnpm they pass, which is why the shim path is used here. That is an environment fact about this machine, not a change in this branch.

Not run: dev/bench.sh (no bench was started for this branch; the test counts reduces rather than timing them) and no real-model end-to-end run (the change is one call site in a pure read path).

Why the read is still correct

The floor is one number for the whole read: floorOf depends on the room and the reader, not on the line, so computing it before the filter and comparing each line to it is the same predicate as before, evaluated fewer times. The clamp (#2754) still compares joinedSeq with room.seq (or the log's last seq), still memoises per room and reader and drops the memo on rejoin, and still warns once per room only when it really clamped. A room whose stored floor is healthy produces no warning, which the new test asserts.

Checkpoint

{
  "pr": 2788,
  "claim": "Dev-1",
  "issue": 2766,
  "summary": "A legacy room's read computed its clamp target once per line: linesFrom called floorOf inside the filter, and floorOf reduces over the whole log when the room has no seq, so an n-line history read was quadratic (20,000 lines: 28852ms, 20000 reduces). linesFrom now resolves the floor once per read and filters with it: the same window, the same clamp and one-time warning, reduces 1 instead of 20000 (7ms). A room with a counter still reduces zero times. New test core/test/room-floor-once.test.js counts the reduces; red first on bd583bd0 was 3 tests / 1 pass / 2 fail, and the three touched suites are 50/50 after the fix. Red first on the base bd583bd0.",
  "files": [
    "core/src/host/room-membership.js",
    "core/test/room-floor-once.test.js",
    "docs/subsystems/core-host.md",
    "changelog.d/2766-room-floor-once.fixed.md",
    "patches/ds-bot/files/src/host/room-membership.js",
    "patches/ds-bot/files/test/room-floor-once.test.js"
  ],
  "checks": {
    "ran": "TZ=UTC npm run verify (DSH_HARNESS set, PATH without pnpm); ARCH_DOCS_BASE=bd583bd0 arch-docs; ds-bot-patches generate/check/canonical; changelog check",
    "result": "green",
    "at": "613cca30b83174571d7237786920f2971e403a07"
  },
  "next": "waiting for the review side's Verdict naming 613cca30b83174571d7237786920f2971e403a07"
}