Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add ychampion/cskill-agents --skill media-block-compaction-prepgit clone --depth 1 https://github.com/ychampion/cskill-agentsWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/ychampion/cskill-agents/media-block-compaction-prep)<a href="https://agentmods.dev/skills/ychampion/cskill-agents/media-block-compaction-prep"><img src="https://agentmods.dev/badge/skills/ychampion/cskill-agents/media-block-compaction-prep/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/ychampion/cskill-agents/media-block-compaction-prep"><img src="https://agentmods.dev/badge/skills/ychampion/cskill-agents/media-block-compaction-prep.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00029 | $0.00316 |
| Opus 5.5 | $0.00012 | $0.00126 |
| Sonnet 5.5 | $0.00006 | $0.00063 |
| Haiku 4.5 | $0.00003 | $0.00032 |
Grade A, and why
media-block-compaction-prep scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 1mo ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
What it actually says
SKILL: Media-Block Compaction Prep
Domain: context-management Trigger: Use when compaction must summarize a session that contains embedded media or document-heavy user messages. Source Pattern: Distilled from reviewed compaction-time media stripping strategies.
Core Method
Walk user messages before compaction and replace heavy media blocks with lightweight placeholders that preserve the fact that the media existed. Keep non-media text and message order intact so the summarizer still sees the conversational structure without paying the full token cost of embedded media. Track whether media was stripped so the summary can note that omitted content existed if needed.
Key Rules
- Replace heavy media with explicit placeholders instead of silently dropping it.
- Preserve message order and all non-media text so downstream heuristics still see the same conversation structure.
- Apply the sanitization before the compaction request so the token savings affect the summary call itself.
Example Application
If a user uploads screenshots and a PDF before a long debugging exchange, replace those media blocks with markers such as [image] or [document] before sending the transcript to the compactor.
Anti-Patterns (What NOT to do)
- Do not delete media with no placeholder.
- Do not rewrite assistant message structure during this prep step.
- Do not leave nested media blocks inside heavy tool results unsanitized.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 1mo ago First seen · 28 lines · 29 tokens per session scan A 22f9bbf5d826
media-block-compaction-prep is a skill published in the GitHub repository ychampion/cskill-agents (36 stars, last pushed 6mo ago), licensed MIT. It adds 29 tokens to every session and 316 once invoked, about $0.0001 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-03.
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