Forge playbook — Context health

Self-improvement substrate: before applying this skill, read learnings.md in this skill's own folder and honor its corrections. After a run that produced a genuine correction, append it there with a date and real evidence — never invent a lesson that did not happen.

The context window is a working desk, not a filing cabinet. Quality does not fade evenly: it holds, then drops at a cliff. This skill keeps a Forge session (Lead, Boss or Workflow agent()) on the good side of that cliff. It is method only: no hooks, no scripts, nothing installed.

Where this skill stops (siblings)

1. Diagnose before you act

Name the pattern first; each has a different fix. Detail and symptoms: references/degradation-patterns.md.

Before you blame the context, rule out the prompt. If the same instruction also fails in a fresh, short context, the instruction is the problem. One bad answer is noise; a repeated drop after the session grew is signal.

2. The four moves (write · select · compress · isolate)

1. Write — put state outside the window: the plan or status doc, _scratch/ (gitignored), research dumps in .claude/forge-research/, lessons via forge-memory. Never loose files in the project root.
2. Select — load only what the step needs: Grep and Glob first, then targeted reads and diffs; no whole-repo dumps; no re-reading a file you just edited.
3. Compress — mask, then summarise (section 3). Summarising beats dropping.
4. Isolate — give an independent part its own fresh context: a Workflow agent() per part with its GOAT route (agentType with fixed model and effort, or explicit model and effort). Splitting costs overhead (each agent loads its own prompt and tools), so it pays off from about three real parts.

3. Mask first, compact second

Observation masking (cheap, low risk). Once a long tool output has given you its point, carry only the point: "build log: 2 errors, both in src/a.ts line 40; full log at _scratch/build.log".

• Never mask: output from the latest turn, anything in an active reasoning chain, and error output while debugging is still open (keep it until the bug is fixed).
• Mask at once: duplicates, boilerplate headers, output already summarised.
• Keep the full text in a file and its path in the summary, so it can be re-read.

Compaction (lossy). Owner rule: compact on your own terms with a focus, around 60 % context use; never wait past 80 % (a model under heavy pressure writes worse summaries). Compact at a task boundary, not in the middle of an edit. Decision table:

Run /compact <focus> with the next step as focus, for example /compact keep: contract, files a.ts b.ts, next = tests.

Anchored summary, not a fresh rewrite. Each compaction adds to the same fixed sections instead of regenerating everything: Intent · Files touched (exact paths) · Decisions (with reason) · Current state · Next steps · Open risks. Keep identifiers verbatim: paths, commit SHAs, error codes, numbers. Never summarise tool schemas or the owner's own words of the ask (forge-scribe keeps those verbatim). Protect the early turns: the task setup and constraints cannot be re-derived later.

4. Placement rule

Stable material first (rules, contract, architecture), working material last (the current file, the failing test, the exact next step). Recall is best at the start and the end, weakest in the middle. When a long document must stay, put its key points before it and its conclusion after it.

5. Working rules from file-based planning

Adapted as rules only (no hooks, no scripts):

• 2-action rule: after every two search, browse or screenshot steps, write the key findings to the plan or _scratch/ file before going on. Images and web pages do not survive compaction; text does.
• Read before you decide: before a major decision, re-read the plan's goal section.
• Update after you act: at the end of a phase mark it done, list the files changed, log the errors.
• Never repeat a failure: the same failing command twice in a row is a defect. Change the approach.
• 3-strike rule for one error: attempt 1 diagnose and fix the cause; attempt 2 a different method; attempt 3 question the assumptions. Then stop and report what you tried. This sits under the GOAT ladder (one escalation per work package) and the recovery policy (safe alternatives before BLOCKED).
• Read or write? Just wrote it: do not re-read. Saw an image or web data: write it down now. New phase or after a gap: read the plan and findings again.

6. After compaction or a restart: prove you still know

Ask yourself these and answer each from a real source (plan doc, FORGE_SNAPSHOT.md, git status, run events), not from memory:

1. Where am I? (current phase or work package)
2. Where am I going? (remaining steps)
3. What is the goal? (the owner's ask, verbatim if possible)
4. What have I learned? (decisions and findings with paths)
5. What have I done? (files changed, checks run with their real result)

Probe questions catch a bad summary: "which file did I change last?", "what was the exact error?", "what did the owner forbid?". If an answer is missing or vague, re-read the source before going on. A summary that looks sure can still be stale: check it against the current ask.

7. Safe restart boundaries

Start a fresh session (or a fresh agent) at a finished task boundary, never at a random token count. Before leaving, persist: accepted scope and decisions · task status and the next task · files changed and the working-tree state · exact verification commands and their outcomes · open questions, risks and approvals still needed. Do not commit or push unless the owner authorised it; otherwise record that the changes are uncommitted. In the new session, read those artifacts and the real git status first, and never infer an approval from an old conversation that no durable file records.

Honesty

Token counts here are estimates unless /context or a measured report shows them. Never claim a compaction "kept everything"; say what was dropped. Thresholds from outside sources go stale with new models — treat them as starting points.

Provenance

• muratcankoylan/Agent-Skills-for-Context-Engineering — paths skills/context-degradation/SKILL.md, skills/context-optimization/SKILL.md, skills/context-compression/SKILL.md; pinned SHA 9ff0c99108b36d3b886defd825d8ac1f47dba374; MIT License, Copyright (c) 2025 Context Engineering Agent Skills Contributors. Taken (rewritten): the five degradation patterns, write/select/compress/isolate, masking rules, the 70–80 % compaction warning, anchored iterative summaries, probe questions, placement rule. Excluded: Python examples, benchmark tables and model-specific thresholds, framework landscape.
• addyosmani/agent-skills — path skills/context-engineering/SKILL.md; pinned SHA 301b02b12bff98e4688e6984af6556802322bbde; MIT License, Copyright (c) 2025 Addy Osmani. Taken (rewritten): what to cut first / protect until the end, compress before dropping, order for recency, restartable session boundaries. Excluded: rules-file templates, MCP integration section.
• OthmanAdi/planning-with-files — path .agents/skills/planning-with-files/SKILL.md; pinned SHA 8eef6dc6540dde5eef3fdc0ac487ad9c48ef3ba5; MIT License, Copyright (c) 2026 Ahmad Adi. Taken (rules only, rewritten): 2-action rule, read before decide, update after act, never repeat failures, 3-strike protocol, read-vs-write matrix, 5-question reboot test. Excluded: all hooks (5 hook events), shell/Python/PowerShell scripts, slash commands, plan-file templates and install steps.
• ECC skills/strategic-compact/SKILL.md — pinned local catalog commit e2b8a51cea2228e515e1c3653effbeb62a2800fa; MIT License, Copyright (c) 2026 Affaan Mustafa. Taken (rewritten): compact at logical boundaries, the phase-transition table, write before compacting, /compact with a focus. Excluded: the suggest-compact.js PreToolUse hook and its settings snippet, env variables, the third-party MCP tool suggestions. The MIT notices above apply to the adapted portions; the full MIT text is at each source repository. Verified 2026-11-05: every GitHub path above was fetched read-only at its pinned SHA from raw.githubusercontent.com (HTTP 200; the GitHub API was unreachable), and the copyright lines were read from each root LICENSE; the ECC catalog was confirmed at e2b8a51 with skills/strategic-compact present. Hidden-Unicode scan of the fetched text: clean.