merge: integrate origin/main (v1.1.0.0) — V1 + Puppeteer parity + /plan-tune

Big merge. Main shipped three releases while this branch was in flight:
- v0.19.0.0 /plan-tune skill (observational layer; dual-track dev profile)
- v1.0.0.0 V1 prompts (simpler, outcome-framed, jargon-glossed) + LOC receipts
- v1.1.0.0 browse Puppeteer parity (load-html, file://, --selector, --scale)

This branch bumps to v1.2.0.0 (above main's v1.1.0.0) per the
branch-scoped-version rule in CLAUDE.md. My "0.19.0.0" CHANGELOG entry
is renamed to "1.2.0.0" and dated 2026-04-18 to land above main's trail.

Conflicts resolved:
- VERSION / package.json: 1.2.0.0
- CHANGELOG.md: preserved my entry at top (renamed), kept main's 1.1.0.0
  / 1.0.0.0 / 0.19.0.0 / 0.18.4.0 trail below in correct order
- .github/docker/Dockerfile.ci: kept my xz-utils + nodejs.org tarball
  fix (real CI bug fix main didn't have); absorbed main's retry loop
  structure for both apt and the tarball curl
- bin/gstack-config: kept both my checkpoint_mode/push section and
  main's explain_level writing-style section
- scripts/resolvers/preamble.ts: kept my submodule refactor as the
  file shape; extracted main's new generateWritingStyle and
  generateWritingStyleMigration into scripts/resolvers/preamble/
  submodules; absorbed main's generateQuestionTuning import
- All generated SKILL.md files: resolved by regen via
  bun run gen:skill-docs --host all (per CLAUDE.md: never hand-merge
  generated files — resolve templates and regen)
- Ship golden fixtures (claude/codex/factory): refreshed

Tier 2 preamble composition now includes all 8 sections: context
recovery, ask-user-format, writing-style, completeness, confusion,
continuous checkpoint, context health, question tuning.

Main also brought new test files from /plan-tune: skill-e2e-plan-tune,
upgrade-migration-v1, v0-dormancy, writing-style-resolver. All absorbed.
468 tests pass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

bin/gstack-config

@@ -51,6 +51,14 @@ CONFIG_HEADER='# gstack configuration — edit freely, changes take effect on ne
 #                           # false = keep WIP commits local only (default)
 #                           # Pushing can trigger CI/deploy hooks — opt in carefully.
 #
+# ─── Writing style (V1) ──────────────────────────────────────────────
+# explain_level: default    # default = jargon-glossed, outcome-framed prose
+#                           #           (V1 default — more accessible for everyone)
+#                           # terse   = V0 prose style, no glosses, no outcome-framing layer
+#                           #           (for power users who know the terms)
+#                           # Unknown values default to "default" with a warning.
+#                           # See docs/designs/PLAN_TUNING_V1.md for rationale.
+#
 # ─── Advanced ────────────────────────────────────────────────────────
 # codex_reviews: enabled    # disabled = skip Codex adversarial reviews in /ship
 # gstack_contributor: false # true = file field reports when gstack misbehaves
@@ -101,6 +109,11 @@ case "${1:-}" in
       echo "Error: key must contain only alphanumeric characters and underscores" >&2
       exit 1
     fi
+    # V1: whitelist values for keys with closed value domains. Unknown values warn + default.
+    if [ "$KEY" = "explain_level" ] && [ "$VALUE" != "default" ] && [ "$VALUE" != "terse" ]; then
+      echo "Warning: explain_level '$VALUE' not recognized. Valid values: default, terse. Using default." >&2
+      VALUE="default"
+    fi
     mkdir -p "$STATE_DIR"
     # Write annotated header on first creation
     if [ ! -f "$CONFIG_FILE" ]; then