feat(extensions): establish canonical goal source (#54, #55)

.pi/.gitignore

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+extensions/
+extensions.installed.sha256
+.extensions-*
+state/
+evidence/
+native-test-*.log

.pi/README.md

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+# Native goal development copy
+
+From this repository, start a fresh native Pi session:
+
+```sh
+bash scripts/goal-dev.sh
+```
+
+Canonical source lives under `extensions/`. The launcher first runs `scripts/sync-dev-extensions.sh`, which installs verified ordinary-file copies under `.pi/extensions/`, then loads only the generated goal extension. Global extensions remain unloaded. The launcher keeps your usual native Pi provider authentication; it copies no credentials. Goal state and new conversation files live under `.pi/state/`, which is ignored by Git. Each process gets a fresh incarnation; `/reload` and `/new` in the same process retain its goal. Restarting Pi does not adopt an earlier process's active goal.
+
+Plain `pi` also discovers `.pi/extensions/goal/index.ts` after project trust, but may load global extensions too. Use the launcher to avoid duplicate `/goal` registrations. This is a local development test, not a sandbox or the managed Mosaic runtime. Docker and `~/.mosaic` are unchanged.
+
+## Try it
+
+1. Set `/goal <a long goal with acceptance criteria>`. This starts work immediately.
+2. Look below the editor for `Goal: Active`. The old above-editor goal widget is gone.
+3. Run bare `/goal`, then press `Alt+G`. Both show the entire stored goal and its status. Tab remains autocomplete.
+4. Use `/goal stop` and `/goal resume`. Expect Paused and Active, or Waiting if an untimed wait remains recorded.
+5. A blocked `goal_report` displays Blocked. A satisfied report displays Complete and retains the full goal for recall without continuing work.
+6. `/goal clear` removes the retained goal. Try `NO_COLOR=1 bash scripts/goal-dev.sh` to check text-only labels.
+
+Use terminal scrollback for recall longer than the screen. At narrow widths Pi may truncate its footer status row; bare `/goal` and Alt+G remain available.
+
+## Checks
+
+```sh
+node --test extensions/goal/test/*.test.ts
+bash scripts/test-extension-package.sh
+python3 scripts/test-goal-native.py
+```
+
+Contract tests use ordinary read-only fixture copies in `test/fixtures/skills-local/`, not live brain files. The executive-update fixture SHA-256 matches the parser's pinned contract, `bbea48a46b1f8da7bc759f86856fb52830b7dde456b826317163c6dc6ccab319`.
+
+`SOURCE-SNAPSHOT.json` records the original external-source baseline, not the edited candidate. No symlinks are used. Never edit `.pi/extensions/`; the sync script refuses to overwrite installation drift. Make changes under `extensions/`, run the checks, and relaunch. To disable the test, stop its Pi process and remove `.pi/extensions/`. Keep `.pi/state/` only if you need local test state.

.pi/SOURCE-SNAPSHOT.json

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+{
+  "snapshotVersion": 1,
+  "copiedAt": "2026-09-06T04:58:22Z",
+  "source": "~/.mosaic/fleet/extensions",
+  "goalTreeSha256": "8853f2b72dde3e87c4573648b9a931c1c75da87ccde995c3224e6d2e707a75f0",
+  "mosaicCoreLibTreeSha256": "d1194dce31209e5773c6cc5ce571cbca3c39b29d943a79dea06665e05d29f319",
+  "symlinks": false,
+  "autoDiscoveredExtensions": ["goal"],
+  "purpose": "Issue #54 native Pi NG development copy; never loaded by Docker"
+}

.pi/goal-dev.sh

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+#!/usr/bin/env bash
+# Compatibility entrypoint for the accepted native test command.
+set -euo pipefail
+cd "$(dirname "${BASH_SOURCE[0]}")/.."
+exec scripts/goal-dev.sh "$@"