[BUG] Compaction happens every few steps for no reason, context is only around 50% of maximum

[TheGoodMorty]

I just updated to the Next release of DSH, and now I notice it keeps going into compaction early and repeats every few steps

[bsmart1120]

Not a coincidence — we hit the same symptom and traced it to the 0.1.7 compaction trigger formula in @deepseek-ai/dsh-compaction-basic:

thresholdTokens = min(contextWindow * thresholdRatio,
                      contextWindow - reservedMaxTokens - headroomTokens)

headroomTokens defaults to 65536 and is an absolute value that does not scale with the window (config.headroomTokens ?? 65536, lib/index.js:63), so the second term wins on any small/medium route and thresholdRatio: 0.8 stops having any effect:

window W	request reserve O	stock trigger	% of W
150,000	32,000	min(120000, 150000-32000-65536) = 52,464	35.0%
126,976	32,000	min(101580, 126976-32000-65536) = 29,440	23.2%
1,000,000	256,000	678,464	67.8%

And @deepseek-ai/dsh-token-meter folds the tool schemas into the measured total (~18K tokens with a plugin-heavy tool set here), so a 150K route has only ~34K of actual conversation budget before compaction fires — which lines up with your "around 50% of maximum" observation.

Measured on our side by decoding ~/.dsh/sessions/**/session.v4.jsonl.zstd and counting compaction/* against step/*: 32 compactions in a 49-step session (roughly one every 1.5 steps), plus compaction/prune events with shadowedRange.start == end that threw away freshly read files (2K–10K tokens each), causing a re-read loop.

Full write-up with the 0.1.5-vs-0.1.7 source diff, impact table, session evidence, the compactIfNeeded prune-before-measure ordering issue, and three suggested fixes: #8079

Workaround until upstream decides: set headroomTokens: 8192 (and explicitly maxTokens: 8192, since its default is taken from headroomTokens) on the compaction-basic row inside the preset file (dsh-web-app/presets/standard.patch.yml, ptc.patch.yml, cordis.patch.yml). Note a profile cordis.patch.yml override targeting the same - id: compaction-basic does not take effect — the dsh-base top-level row is disabled: true under a preset, so the override lands on the disabled row while the preset's own copy keeps the default. That puts a 150K route back at min(120000, 150000-32000-8192) = 109,808 (~73%).