/canvas-update

name: canvas-update
description: "Update canvas sections with new evidence. Ensures canvas stays current as the single source of truth."
metadata:
  instruction_budget: "12"
  framework_dependency: "mycelium"
  framework_dependency_note: "This skill is designed to run within the Mycelium framework (https://github.com/haabe/mycelium). Standalone use will skip the canvas state, theory gates, and harness behavior the skill assumes. Install: /plugin install mycelium@haabe-mycelium."

Canvas Update

Preflight: Read target canvas file(s) before any Write/Edit

**Hard rule.** Before issuing `Write` or `Edit` against any `.claude/canvas/*.yml`, use the **Read tool** on that file in this session. Claude Code's Read-before-Write check requires the `Read` tool specifically — `cat`/`head`/`grep` via Bash do NOT satisfy it.

**Edit vs Write — different cost profiles** (verified 2026-05-14):

• **`Edit`** (exact-string replacement): `Read` with `limit: 1` satisfies the check at ~50 tokens. State-tracking is per-file, not per-byte — subsequent `Edit` calls work anywhere in the file. Use this for partial updates against large canvas files (e.g., `purpose.yml` at 800+ lines).
• **`Write`** (full replacement): do a **full Read** first. Write obliterates the file; you should see what you're about to replace. The `limit:1` shortcut is *not* appropriate here.

**ID-bearing entries — scan the ID space before assigning** (added 2026-05-15, v0.23.19): When adding a new component, opportunity, solution, or any other ID-bearing entry to a canvas file, run a Bash grep first to confirm the next ID in your prefix sequence is actually free:

grep -o "<prefix>-[0-9][0-9]*" .claude/canvas/<file>.yml | sort -u -t- -k2 -n | tail -3

Replace `<prefix>` with the canvas's ID prefix (`comp` for landscape, `opp` for opportunities, `sol` for solutions, `ht` for human-tasks, etc.). Then pick the next free integer, **matching the zero-padding already used in that file**. The sort is NUMERIC (`-t- -k2 -n`) rather than lexical, and that is not pedantry: a plain `sort -u` orders `ht-1` after `ht-080`, so on a canvas with inconsistent padding it reports the wrong maximum and the next ID collides. Verified on the dogfood repo 2026-08-13, where lexical sort returned `ht-1` as the highest human-task ID against an actual `ht-080`. `grep -o` is also deliberate: it matches IDs wherever they appear, including cross-references and prose, so an ID that was promised somewhere but not yet defined is not handed out twice. `validate_canvas.py` has a duplicate-ID check (lines 230-239) that catches the failure on CI, but a duplicate can persist in the working tree for days if CI isn't run between edit and discovery — see roadmap-repo `corrections.md` 2026-05-15 "Duplicate canvas ID created in landscape.yml" for the worked example.

Original failure mode: anti-pattern #7 instance #5, 2026-05-09 — agent conflated Bash `head` with the Read tool, lost ~14k tokens to a Write-fail → remedial-full-Read → re-Write loop. The `limit:1` discipline (graduated 2026-05-14, v0.23.18) prevents the second-order cost where the agent *correctly* follows the rule but full-Reads every time. The ID-scan discipline (graduated 2026-05-15, v0.23.19) prevents the related class where the agent reads enough of the file to satisfy the Edit check but not enough to see existing ID assignments — kin to anti-pattern #8 (Stale State Read).

If this skill writes to multiple canvas files, register each one first (limit:1 for Edit-only paths; full Read for Write paths) AND ID-scan any prefix you intend to assign.

See `CLAUDE.md` *Canvas writes — Read before Write* for the canonical rule.

Rules

1. **Never update without evidence** -- every canvas change must have a source 2. **Maintain cross-file consistency** -- if you update opportunities.yml, check if north-star.yml or gist.yml need updates too 3. **Log the update** -- add an entry to .claude/harness/decision-log.md explaining what changed and why

Which Canvas File for Which Information

> **Routing rule (Hick's Law, added v0.39.18)**: when the new information could plausibly fit multiple canvas files, recommend ONE primary destination based on the information's PRIMARY type (the "why" of the data), with at-most-one secondary cross-reference. Do not present a flat list of candidate files for the user to choose from; that manufactures decision-tax. The table below maps each information type to its canonical canvas file — pick the row whose information type best describes what's being added, not the row whose source-theory the agent finds most interesting.

| Information Type | Canvas File | Source | |-----------------|-------------|--------| | Purpose, mission, why | purpose.yml | Sinek | | North Star metric, inputs | north-star.yml | North Star Framework | | BVSSH health scores | bvssh-health.yml | Smart | | Value chain, competitive | landscape.yml | Wardley | | Team structure | team-shape.yml | Skelton | | User opportunities, OST | opportunities.yml | Torres | | User needs map | user-needs.yml | Allen | | Goals, ideas, steps | gist.yml | Gilad | | Service quality scores | services.yml | Downe | | Go-to-market, positioning | go-to-market.yml | Lauchengco | | Delivery performance | dora-metrics.yml | Forsgren | | Security threats | threat-model.yml | OWASP | | Privacy assessment | privacy-assessment.yml | GDPR/PbD | | Trust architecture | trust-signals.yml | Digital Trust | | Jobs to be done | jobs-to-be-done.yml | Christensen | | Bounded contexts | bounded-contexts.yml | Evans (DDD) | | Value stream map | value-stream.yml | Rother & Shook (VSM) | | Content delivery metrics | content-metrics.yml | v0.11.0 | | AI tool delivery metrics | ai-tool-metrics.yml | v0.11.0 | | Service delivery metrics | service-metrics.yml | v0.11.0 | | Human task tracking | human-tasks.yml | v0.11.0 | | Archived/discarded solutions | archived-solutions.yml | v0.12.0 | | Leaf lifecycle calibration | cycle-history.yml | v0.12.0 |