cc-os/docs/plans/b3-memsearch-injection-review.md

B3 — memsearch SessionStart injection cost review

Reviewed 2026-07-08. memsearch v0.4.6 (installed) / v0.4.11 (also cached, not yet installed). Plugin: memsearch@memsearch-plugins.

What gets injected

hooks/session-start.sh (both cached versions, logic unchanged 0.4.6→0.4.11) builds a # Recent Memory block on every SessionStart and returns it as additionalContext:

• Finds the daily memory files under $MEMORY_DIR (~/.memsearch/memory/YYYY-MM-DD.md), sorted by filename descending, and takes the 2 most recent.
• For each of those 2 files, greps lines matching ^(#{2,4} |- ) (headings + bullets) and takes the first 40 matching lines (head -40).
• Concatenates both files' extracts under one # Recent Memory heading and returns it.

This is entirely hardcoded (head -2, head -40) in the shell script — there is no per-file/per-line/byte cap that's user-configurable.

Measurements (cc-os project, last ~7 days of session transcripts)

Extracted the additionalContext string from every SessionStart hook event whose payload contained # Recent Memory, across ~/.claude/projects/-home-jared-dev-cc-os/*.jsonl (61 SessionStart events found in that window — heavy usage during the WS2/WS4 eval loops, so this sample is skewed toward busy days, not a quiet baseline).

Stat	chars	approx tokens (÷4)
min	5,976	~1,494
median	11,721	~2,930
avg	11,978	~2,995
max	15,407	~3,852

This roughly confirms the ~13 KB figure already observed. Size scales with how many ##/###/bullet lines the 2 most recent daily files accumulated that day — on a day with a lot of sessions/subagent activity (like the recent eval-loop days), each daily file alone can hit the 40-line cap, so the injection saturates near its structural ceiling (2 files × 40 lines × ~150–200 chars/line ≈ 12,000–16,000 chars), matching the observed range.

Caveat: this is a per-project sample from one heavy-usage repo (cc-os) over 7 days; other projects' daily files will differ, and this sampling method (string-matching the raw jsonl, not a documented API) is the best available without deeper memsearch internals — reasonably solid since the hook's exact output string was recovered from real transcripts, not estimated.

Config surface found

Read skills/memory-config/SKILL.md (both cached versions) and hooks/session-start.sh directly. Findings:

• The documented TOML config surface (plugins.claude-code.summarize, .project_review, .user_profile, .memory_to_skill, [llm.providers.*], [prompts]) controls summarization, maintenance artifacts (PROJECT.md/USER.md), skill distillation, and provider routing — none of it touches the SessionStart recall injection.
• No [plugins.claude-code.session_start] or equivalent section exists in the documented schema, and none of the constants used by the injection logic (head -2 file count, head -40 line count, the ^(#{2,4} |- ) grep pattern) appear anywhere in config.toml, memsearch config list --resolved/--global/--project, or the SKILL.md. They are hardcoded in hooks/session-start.sh itself.
• The only adjacent, real lever is memory file density: since the cap is by line count (not token count) over headings+bullets, whatever produces terse vs. verbose daily-file bullets (the Stop-hook summarizer, governed by plugins.claude-code.summarize.model, defaults to haiku) indirectly controls how much of the 40-line budget per file is "real signal" vs. how many days of content get squeezed out.

Recommendation

No first-class cap/trim setting exists in memsearch's config schema for this injection. The two concrete options, in preference order:

1. Workaround, no code change (recommended to try first): the injection is driven purely by memory-file content density, not by any setting. If daily files are noisy (e.g. many short low-signal bullets from busy multi-session days, as in the cc-os sample), the Stop-hook summarizer producing those bullets is the actual place to add discipline — tightening what counts as bullet-worthy would shrink the 40-line/file budget's real size without touching the plugin. This is a memsearch summarizer/prompt-quality issue, not a session-cost cap.
2. Direct edit, unsupported (only if (1) is insufficient): hand-edit the cached hooks/session-start.sh at ~/.claude/plugins/cache/memsearch-plugins/memsearch/<version>/hooks/session-start.sh, lowering head -2 → head -1 (halves injection size, roughly ~6–8 KB/day instead of ~12–15 KB) and/or head -40 → a smaller value (e.g. 20). Expected savings: cutting to 1 file × 20 lines would drop the typical injection from ~11–15 KB (~2,900–3,850 tokens) to roughly ~3 KB (~750 tokens), a ~75% reduction. Caveat: this is an unmanaged edit to plugin-cache source — it will be silently overwritten on the next claude plugin update memsearch / cache refresh, is not upstream-supported, and isn't a "setting" in the config-surface sense the task asked to identify. Treat it as a stopgap, not a durable fix; if this repo wants a durable cap, the change belongs upstream in zilliztech/memsearch (file an issue/PR to add a [plugins.claude-code.session_start] max_files / max_lines_per_file config section) rather than as a local hack here.

No setting was applied — this is a review/recommendation only per the task.