Forge playbook — Snapshot (context-continuity snapshot system)

Self-improvement substrate (wp-skill-evals): 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 (an owner fix, a false assumption caught, a preference stated), append it to learnings.md with a date and real evidence — never invent a lesson that didn't happen.

Owner request: "bij elke 50% context een snapshot.md zodat er geen memory wordt vergeten… en dan een uitgebreid rapport zodat de agents nog weten wat we maken — dit geldt ook voor globaal." There is no context-percentage available to a hook (a closed Claude Code feature request — the only percentage lives in the separate statusline channel, context_window.used_percentage, which no hook can read). This system never fabricates or estimates one. Instead it fires on the real, honest signals: a PreCompact hook (the genuine "context is about to be compacted" event), a phase boundary, or an explicit manual call.

What it does

1. forge-bin/forge-snapshot.cjs — the generator. write([--run <id>] [--reason ...]) regenerates .claude/FORGE_SNAPSHOT.md from real sources: FORGE_MEMORY.md's latest status block, FORGE_TASK_HISTORY.md's latest entry, tasks/WORK_PACKAGES.md's latest mission block, FORGE_DECISIONS.md's most recent rows, the newest run's events.jsonl (done/in-progress buckets, each with a real evidence pointer), command-center/mission/TODO_GRAPH.md or WORK_PACKAGES.md's WP-ID/Status lines (open items), git log/branch/dirty state, FORGE_VERSION.json, and the newest forge-runs/*/doctor.json. Ten fixed sections: Mission · Why · Current state · Key decisions · Active constraints · Key file paths · Known gaps/limitations · Next actions · Evidence pointers · Honesty footer. check([--max-age-hours N]) is a read-only staleness probe (for the doctor or a manual check).
2. forge-bin/forge-snapshot-marker.cjs — the PreCompact hook target (matchers manual+auto). Writes .claude/.forge-snapshot-due.json and immediately calls forge-snapshot.cjs's write() so a real skeleton exists even if the session ends before the next step runs. Never blocks compaction (always exits 0), never prints anything to stdout, never prints a secret.
3. forge-bin/forge-snapshot-reinject.cjs — the SessionStart hook target, matcher compact. If the due-marker exists, prints a short (<= ~600 tokens) block — Mission + Current state + Next actions + an explicit instruction to refresh sections 3-9 — to stdout, which Claude Code re-injects directly into context (the one official re-injection point this whole system relies on). Then deletes the marker. No marker -> prints nothing, exits 0.
4. forge-bin/forge-snapshot-settings.cjs — the one-time, idempotent .claude/settings.json MERGE helper used to wire the two hooks above without ever clobbering pre-existing hooks/keys (apply --target <path> --marker-command "<cmd>" --reinject-command "<cmd>" [--backup]).

Anti-drift (the core design decision)

• Section 3 ("Current state") is ALWAYS re-derived fresh from source-of-truth on every regeneration — never patched forward from a previous snapshot. Changing events.jsonl or TODO_GRAPH.md between two write() calls changes the output; nothing is ever carried over except what section-1 explicitly preserves.
• Section 1 ("Mission") is the one deliberate exception — preserved VERBATIM across regenerations. It is read from an existing <!-- MISSION:BEGIN -->...<!-- MISSION:END --> marker if the current FORGE_SNAPSHOT.md already has one; else migrated verbatim from a pre-existing hand-written snapshot's own first ## section (a one-time migration path so a hand-authored stopgap's mission survives the switch to this tool); else derived from FORGE_MEMORY.md's latest status heading; else an honest, clearly-marked TODO for a human/agent to fill in — never guessed prose.

Size discipline

Target <= ~2000 tokens of prose (chars/4 heuristic — approximate, not a real tokenizer, and reported honestly as approxTokens rather than presented as exact). Long things are paths, never inlined. Every generated section (2..9 — Mission is exempt) that would exceed its own character budget is cut with an explicit "(truncated — see <path>)" marker rather than growing unbounded.

Honesty

Every generated claim carries a real evidence pointer (a relative path, optionally with an event type/heading) or is explicitly marked in the Honesty footer's "unknown/missing" list — never a bare, unattributed assertion. No context-window percentage is ever fabricated or estimated anywhere in this system.

Wiring (opt-in, already applied 2026-07-29 — see HOOKS_OPT_IN.md for the live record)

• Project-local .claude/settings.json: PreCompact (matchers manual+auto) -> forge-snapshot-marker.cjs; SessionStart (matcher compact) -> forge-snapshot-reinject.cjs.
• Global ~/.claude/settings.json: the same two events, appended alongside the 2 pre-existing global hooks (hotspot-lock, secret-scrub) and every other pre-existing entry — proven preserved byte-for-byte by forge-snapshot-settings.test.cjs's load-bearing safety suite. The global hook commands point at the GLOBAL minimal mirror (~/.claude/forge-bin/forge-snapshot-{marker,reinject}.cjs), which resolves the target project's root from CLAUDE_PROJECT_DIR (or cwd) and dynamically requires that project's own .claude/forge-bin/forge-snapshot.cjs — a project with no Forge install degrades silently (no output, exit 0).

When to use

• Automatically: the wired PreCompact/SessionStart(compact) hooks fire on a real compaction.
• Manually: /forge snapshot (phase boundary, or whenever the owner wants a fresh, evidenced snapshot without waiting for a compaction) -> node .claude/forge-bin/forge-snapshot.cjs write --reason phase.
• Suggest /compact with a short focus note at a logical boundary (a phase just finished, or before an unrelated task) — around 60% context use — never in the middle of a task.
• node .claude/forge-bin/forge-snapshot.cjs check --max-age-hours 24 to probe staleness (e.g. from a doctor pass or before a long unattended run).

Skills / commands

forge-bin/forge-snapshot.cjs (write/check), forge-bin/forge-snapshot-marker.cjs (PreCompact target), forge-bin/forge-snapshot-reinject.cjs (SessionStart target), forge-bin/forge-snapshot-settings.cjs (settings.json merge helper), .claude/FORGE_SNAPSHOT.md (the generated artifact — never hand-edit sections 2-10; edit only the text between the MISSION markers to change the Mission), .claude/.forge-snapshot-due.json (transient marker, deleted on consumption).

Fan-out & flow

1 agent, no team. This is a deterministic, zero-dependency CLI + two small hook targets — not a multi-agent task. Any Boss doing build/fix work can call write --reason phase directly at a natural checkpoint.

Ship-readiness (unique)

Never fabricates a context percentage; never blocks compaction/session-start (both hook targets always exit 0); never prints a secret (FORGE_SNAPSHOT.md only ever holds paths/pointers/short evidenced text, never raw file bodies or credentials); the settings.json merge is proven idempotent and non-destructive by a dedicated test suite before being applied to the real global config; degrades silently in a project with no Forge install.