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>

SKILL.md

@@ -147,6 +147,29 @@ prompts from sub-sessions.
 After handling JUST_UPGRADED (prompts done or skipped), continue with the skill
 workflow.
 
+If `WRITING_STYLE_PENDING` is `yes`: You're on the first skill run after upgrading
+to gstack v1. Ask the user once about the new default writing style. Use AskUserQuestion:
+
+> v1 prompts = simpler. Technical terms get a one-sentence gloss on first use,
+> questions are framed in outcome terms, sentences are shorter.
+>
+> Keep the new default, or prefer the older tighter prose?
+
+Options:
+- A) Keep the new default (recommended — good writing helps everyone)
+- B) Restore V0 prose — set `explain_level: terse`
+
+If A: leave `explain_level` unset (defaults to `default`).
+If B: run `~/.claude/skills/gstack/bin/gstack-config set explain_level terse`.
+
+Always run (regardless of choice):
+```bash
+rm -f ~/.gstack/.writing-style-prompt-pending
+touch ~/.gstack/.writing-style-prompted
+```
+
+This only happens once. If `WRITING_STYLE_PENDING` is `no`, skip this entirely.
+
 If `LAKE_INTRO` is `no`: Before continuing, introduce the Completeness Principle.
 Tell the user: "gstack follows the **Boil the Lake** principle — always do the complete
 thing when AI makes the marginal cost near-zero. Read more: https://garryslist.org/posts/boil-the-ocean"
@@ -766,7 +789,8 @@ Refs are invalidated on navigation — run `snapshot` again after `goto`.
 |---------|-------------|
 | `back` | History back |
 | `forward` | History forward |
-| `goto <url>` | Navigate to URL |
+| `goto <url>` | Navigate to URL (http://, https://, or file:// scoped to cwd/TEMP_DIR) |
+| `load-html <file> [--wait-until load|domcontentloaded|networkidle]` | Load a local HTML file via setContent (no HTTP server needed). For self-contained HTML (inline CSS/JS, data URIs). For HTML on disk, goto file://... is often cleaner. |
 | `reload` | Reload page |
 | `url` | Print current URL |
 
@@ -817,7 +841,7 @@ Refs are invalidated on navigation — run `snapshot` again after `goto`.
 | `type <text>` | Type into focused element |
 | `upload <sel> <file> [file2...]` | Upload file(s) |
 | `useragent <string>` | Set user agent |
-| `viewport <WxH>` | Set viewport size |
+| `viewport [<WxH>] [--scale <n>]` | Set viewport size and optional deviceScaleFactor (1-3, for retina screenshots). --scale requires a context rebuild. |
 | `wait <sel|--networkidle|--load>` | Wait for element, network idle, or page load (timeout: 15s) |
 
 ### Inspection
@@ -844,7 +868,7 @@ Refs are invalidated on navigation — run `snapshot` again after `goto`.
 | `pdf [path]` | Save as PDF |
 | `prettyscreenshot [--scroll-to sel|text] [--cleanup] [--hide sel...] [--width px] [path]` | Clean screenshot with optional cleanup, scroll positioning, and element hiding |
 | `responsive [prefix]` | Screenshots at mobile (375x812), tablet (768x1024), desktop (1280x720). Saves as {prefix}-mobile.png etc. |
-| `screenshot [--viewport] [--clip x,y,w,h] [selector|@ref] [path]` | Save screenshot (supports element crop via CSS/@ref, --clip region, --viewport) |
+| `screenshot [--selector <css>] [--viewport] [--clip x,y,w,h] [--base64] [selector|@ref] [path]` | Save screenshot. --selector targets a specific element (explicit flag form). Positional selectors starting with ./#/@/[ still work. |
 
 ### Snapshot
 | Command | Description |