Kjell Tore Guttormsen
8376dab83f
Fase 4 token-opt, Item 1 of gap-review NEXT STEP #2. The prompt-cache pattern corpus + TOK scanner were frozen at an "Opus 4.7" framing after CC shipped Opus 4.8 (default, 2.1.154) and Fable 5 (2.1.170). Model-era facts re-verified against the official changelog cache before editing. The patterns are properties of prompt-caching, not of any model, so mechanic text is now model-neutral with a single "current default: Opus 4.8" anchor — preventing a re-freeze at the next model bump. - rename knowledge/opus-4.7-patterns.md -> prompt-cache-patterns.md (git mv, history preserved); 6 reference sites updated - TOK scanner: line-318 finding text (human-facing) made model-neutral; header + cache-prefix-scanner + CLI comments refreshed - configuration-best-practices.md body + footnote 4.7 -> 4.8 - human-facing docs: commands/{tokens,help,manifest}.md, project CLAUDE.md, README, docs/scanner-internals.md - gap-matrix row marked DONE; future Items 2/3 retargeted to new filename Failing-test-first (Iron Law): +2 knowledge staleness guards (era-anchor + no-refreeze) +1 scanner assertion (no stale model anchor in finding text). Suite 853 -> 856 green; zero snapshot drift; self-audit A(97) PASS. CHANGELOG / v5 plan / ratified gap-plan keep historical opus-4.7-patterns refs (correct record of past state). Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01Ter3E2JSi1Khgmuf2kady8
58 lines
3.9 KiB
Markdown
58 lines
3.9 KiB
Markdown
# Prompt-Cache Configuration Patterns
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> Token-efficiency patterns for current Claude Code (defaults to Opus 4.8; Fable 5 is the top-capability model). Detection IDs map to TOK scanner findings.
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> Sources: research/01-opus-47-features-token-efficiency.md (Topic 1), research/04-prompt-caching-patterns.md (Topic 4). Patterns verified 2026-04-19; model-era anchor refreshed 2026-06-18.
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Current Claude Code defaults to Opus 4.8 (Fable 5 is the top-capability model).
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On these models the cost ceiling per turn is high and both the context window
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and prompt-cache window are large, so cache reuse and tool-schema discipline
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are the dominant levers for keeping a session affordable. These patterns are
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properties of prompt-caching itself, not of any single model — they are
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structural and detectable statically by reading config files without running a
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session. Cache hit-rate measurement requires runtime telemetry and is
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explicitly out of scope.
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| # | Pattern | Detection (ID) | Severity | Fix |
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|---|---------|----------------|----------|-----|
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| 1 | Cache-breaking volatile top-of-file content in CLAUDE.md (timestamps, session ids, rolling activity logs above stable content) | CA-TOK-001 | medium | Move volatile sections to the bottom of CLAUDE.md, or extract to an `@import`-ed file that lives outside the prompt-cache prefix. Keep the first 30 lines stable across turns. |
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| 2 | Redundant tool/permission declarations in settings.json (e.g., both `"Read"` and `"Read(**)"`, duplicate Bash matchers, overlapping glob patterns) | CA-TOK-002 | low | Deduplicate the `permissions.allow` and `permissions.deny` arrays. Prefer the most specific entry that still grants the intended access. Each duplicate entry inflates the tool-schema payload sent on every turn. |
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| 3 | Deep `@import` chain in CLAUDE.md (more than 2 hops, e.g., A → B → C → D) | CA-TOK-003 | medium | Flatten the chain to ≤ 2 hops. Each `@import` boundary fragments the prompt-cache prefix; deeply chained imports defeat caching for the deepest content even when it never changes. |
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> The v4 sonnet-era signature pattern was removed in v5 F5 — too noisy and not
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> actionable. Hotspots ranking and per-pattern findings cover the same ground
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> with concrete, file-anchored signal.
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## Detection notes
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- **Pattern 1 (cache-breaking)** is detected by inspecting the first ~30 lines
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of CLAUDE.md for tokens that look volatile: literal `{timestamp}`, `{uuid}`,
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`{date}`, `{session}` placeholders, or runs of ISO-timestamp-prefixed lines.
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The scanner does not attempt to verify cache-hit rate; it flags the *shape*
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of content that empirically defeats prompt-cache reuse.
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- **Pattern 2 (redundant tools)** is detected by flattening the
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`permissions.allow` and `permissions.deny` arrays and looking for entries
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that are strict subsets of broader entries (e.g., `Bash(npm test)` when
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`Bash(*)` is also present), or exact duplicates.
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- **Pattern 3 (deep imports)** uses the existing IMP scanner's chain depth as
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the input — anything > 2 hops triggers TOK-003 as well as the IMP finding.
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## Threshold calibration
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All thresholds in this catalogue are **structural** — derived from the
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existing `estimateTokens(bytes, kind)` heuristic in
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`scanners/lib/active-config-reader.mjs:29-39`. They are intentionally
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conservative until Topic 3 (token-cost model) research is complete. When
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Topic 3 lands, severities for patterns 1–3 will be re-tuned.
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The `estimateTokens` heuristic uses ~4 bytes per token for markdown content,
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which is conservative but unverified against an authoritative tokenizer.
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All token counts surfaced by the TOK scanner carry an implicit ±20%
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uncertainty band.
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## Severity Scale
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| Severity | Meaning |
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|----------|---------|
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| medium | Materially inflates token cost per turn (cache miss, schema bloat) |
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| low | Detectable inefficiency that compounds across long sessions |
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| info | Informational signal — no action required, may indicate room for optimisation |
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