feat: Pipeline Settings M1 — per-step model picker, system instructions, agent prompts (#170, v0.23.0)

Additive per-step Pipeline Settings page. Reuses the existing model_select picker + versioned prompt registry; no migration. QA APPROVE for eea4968; CI green.

Agent-Session: pipeline-settings-m1-merge

CHANGELOG.md

@@ -5,6 +5,76 @@ All notable changes to PRAutoBlogger will be documented in this file.
 Format follows [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project uses [Semantic Versioning](https://semver.org/).
 
+## [0.23.0] - 2026-06-22
+
+### Added
+- **Pipeline Settings (M1 — additive):** New "Pipeline" wp-admin submenu page
+  (`prautoblogger-pipeline`) with a step rail covering all LLM stages: Research,
+  Analysis, Writer, Editorial, Image. Per-step panels expose the existing model
+  picker (`PRAutoBlogger_OpenRouter_Model_Field`), system-instruction editor, and
+  agent-prompt editor(s) — all bound to the live versioned prompt registry
+  (`PRAutoBlogger_Prompt_Registry`). Saving a prompt creates a new immutable version;
+  reset-to-default available. Active version shown per panel. Writer panel marks
+  inactive sub-stage prompts. No existing Settings sections changed in M1 (both
+  surfaces edit the same options / prompts table).
+- **`get_stages_for_setting()` extended (text→text only):** `prautoblogger_research_model →
+  [research, llm_research]` added for stage-accurate cost-preview. Image model
+  cost preview intentionally omitted (shows static $/image price in picker trigger
+  instead — token-based formula does not apply).
+- New files: `includes/admin/class-pipeline-settings-page.php`,
+  `class-pipeline-settings-renderer.php`, `class-pipeline-settings-save-handler.php`,
+  `class-pipeline-settings-step-map.php`; `assets/css/pipeline-settings.css`;
+  `assets/js/pipeline-settings.js`; `templates/admin/pipeline-settings-page.php`;
+  `CONTEXT.md` (domain glossary, DoD v1.2.0 §7).
+
+### Fixed (QA REQUEST-CHANGES — commit e6550e1)
+- **Model save POST key (P1-1):** `handle_model_save()` now reads the model value
+  from `$_POST[$option_name]` — the key that `PRAutoBlogger_OpenRouter_Model_Field::render()`
+  emits as `<input name="$option_name">` and that `model-picker.js` writes to by DOM id.
+  The old code read `$_POST['model_id']`, which was never present in the POST body,
+  silently overwriting the stored model with an empty string on every "Save Model" click.
+  Removed the dead `prautoblogger:model_selected` event listener in `pipeline-settings.js`
+  (the event was never fired by `model-picker.js`).
+- **Renderer: no business logic in template (P2-3):** `PRAutoBlogger_Cost_Reporter`
+  instantiation moved from `pipeline-settings-page.php` template into
+  `Renderer::render()`; template now receives `$view['monthly_spend']` and
+  `$view['budget']` as plain scalars.
+- **Renderer: dead DB query removed (P2-2):** `$all_versions` assignment in
+  `build_step_data()` removed (it triggered a `SELECT * FROM wp_prautoblogger_prompts`
+  query on every page load but the result was never used).
+- **Image cost-preview dead config resolved (P2-1):** Removed unreachable
+  `prautoblogger_image_model → [image_a, image_b]` map entry from
+  `get_stages_for_setting()` and added a comment explaining the intentional design.
+
+### Docs
+- **CONVENTIONS.md (P1-2):** Added `## How To: Add a New Pipeline-Style Admin Page`
+  section documenting the four-class split, registration priority, renderer contract,
+  POST key convention for the model picker, nonce/cap pattern, allowlist enforcement,
+  prompt key slug round-trip, and test requirements.
+- **CONTEXT.md (P2-4):** Created root domain glossary covering all new Pipeline
+  Settings terms (step, step rail, step panel, pipeline-ui, system instruction,
+  agent prompt, system_key, agent_key, prompt key, prompt slug, reset-to-default,
+  step map, save handler) and prior prompt-registry terms.
+
+### Tests
+- **PHPUnit (P1-3):** Added `tests/unit/Admin/PipelineSettingsSaveHandlerTest.php`
+  covering allowlist enforcement (unknown option/slug rejected), correct POST key
+  reading (`$_POST[$option_name]` not `$_POST['model_id']`), capability gate,
+  nonce gate, and GET idle return.
+- **PHPUnit (P1-3):** Added `tests/unit/Admin/PipelineSettingsStepMapTest.php`
+  covering `allowed_prompt_keys()` / `allowed_model_options()` regression guards,
+  step field completeness, unique step ids, slug round-trip for simple and
+  underscore-containing keys, and `find()` behaviour.
+- **PHPUnit fix:** Removed invalid `Brain\Monkey\Functions\when()` stub for
+  `PRAutoBlogger_Prompt_Registry_Writer::create_version` in
+  `PipelineSettingsSaveHandlerTest::test_handle_prompt_save_rejects_unknown_slug`.
+  Brain\Monkey's `Functions\when()` stubs only global PHP functions, not static
+  class methods; the stub was also unnecessary because the allowlist rejection
+  returns before `create_version()` is ever reached.
+- **CONVENTIONS.md fix:** Corrected slug example for keys containing underscores:
+  `content.single_pass` → `content-single_pass` (not `content-single-pass`);
+  `sanitize_key()` preserves underscores so the round-trip is unambiguous.
+
 ## [Unreleased - Internal]
 
 ### Internal