feat: make model profiles runtime-aware for Codex/non-Claude runtimes (closes #2517) (#2609)

* feat: make model profiles runtime-aware for Codex/non-Claude runtimes (closes #2517)

Adds an optional top-level `runtime` config key plus a
`model_profile_overrides[runtime][tier]` map. When `runtime` is set,
profile tiers (opus/sonnet/haiku) resolve to runtime-native model IDs
(and reasoning_effort where supported) instead of bare Claude aliases.

Codex defaults from the spec:
  opus   -> gpt-5.4        reasoning_effort: xhigh
  sonnet -> gpt-5.3-codex  reasoning_effort: medium
  haiku  -> gpt-5.4-mini   reasoning_effort: medium

Claude defaults mirror MODEL_ALIAS_MAP. Unknown runtimes fall back to
the Claude-alias safe default rather than emit IDs the runtime cannot
accept. reasoning_effort is only emitted into Codex install paths;
never returned from resolveModelInternal and never written to Claude
agent frontmatter.

Backwards compatible: any user without `runtime` set sees identical
behavior — the new branch is gated on `config.runtime != null`.

Precedence (highest to lowest):
  1. per-agent model_overrides
  2. runtime-aware tier resolution (when `runtime` is set)
  3. resolve_model_ids: "omit"
  4. Claude-native default
  5. inherit (literal passthrough)

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

* fix(#2517): address adversarial review of #2609 (findings 1-16)

Addresses all 16 findings from the adversarial review of PR #2609.
Each finding is enumerated below with its resolution.

CRITICAL
- F1: readGsdRuntimeProfileResolver(targetDir) now probes per-project
  .planning/config.json AND ~/.gsd/defaults.json with per-project winning,
  so the PR's headline claim ("set runtime in project config and Codex
  TOML emit picks it up") actually holds end-to-end.
- F2: resolveTierEntry field-merges user overrides with built-in defaults.
  The CONFIGURATION.md string-shorthand example
    `{ codex: { opus: "gpt-5-pro" } }`
  now keeps reasoning_effort from the built-in entry. Partial-object
  overrides like `{ opus: { reasoning_effort: 'low' } }` keep the
  built-in model. Both paths regression-tested.

MAJOR
- F3: resolveReasoningEffortInternal gates strictly on the
  RUNTIMES_WITH_REASONING_EFFORT allowlist regardless of override
  presence. Override + unknown-runtime no longer leaks reasoning_effort.
- F4: runtime:"claude" is now a no-op for resolution (it is the implicit
  default). It no longer hijacks resolve_model_ids:"omit". Existing
  tests for `runtime:"claude"` returning Claude IDs were rewritten to
  reflect the no-op semantics; new test asserts the omit case returns "".
- F5: _readGsdConfigFile in install.js writes a stderr warning on JSON
  parse failure instead of silently returning null. Read failure and
  parse failure are warned separately. Library require is hoisted to top
  of install.js so it is not co-mingled with config-read failure modes.
- F6: install.js requires for core.cjs / model-profiles.cjs are hoisted
  to the top of the file with __dirname-based absolute paths so global
  npm install works regardless of cwd. Test asserts both lib paths exist
  relative to install.js __dirname.
- F7: docs/CONFIGURATION.md `runtime` row no longer lists `opencode` as
  a valid runtime — install-path emission for non-Codex runtimes is
  explicitly out of scope per #2517 / #2612, and the doc now points at
  #2612 for the follow-on work. resolveModelInternal still accepts any
  runtime string (back-compat) and falls back safely for unknown values.
- F8: Tests now isolate HOME (and GSD_HOME) to a per-test tmpdir so the
  developer's real ~/.gsd/defaults.json cannot bleed into assertions.
  Same pattern CodeRabbit caught on PRs #2603 / #2604.
- F9: `runtime` and `model_profile_overrides` documented as flat-only
  in core.cjs comments — not routed through `get()` because they are
  top-level keys per docs/CONFIGURATION.md and introducing nested
  resolution for two new keys was not worth the edge-case surface.
- F10/F13: loadConfig now invokes _warnUnknownProfileOverrides on the
  raw parsed config so direct .planning/config.json edits surface
  unknown runtime values (e.g. typo `runtime: "codx"`) and unknown
  tier values (e.g. `model_profile_overrides.codex.banana`) at read
  time. Warnings only — preserves back-compat for runtimes added
  later. Per-process warning cache prevents log spam across repeated
  loadConfig calls.

MINOR / NIT
- F11: Removed dead `tier || 'sonnet'` defensive shortcut. The local
  is now `const alias = tier;` with a comment explaining why `tier`
  is guaranteed truthy at that point (every MODEL_PROFILES entry
  defines `balanced`, the fallback profile).
- F12: Extracted resolveTierEntry() in core.cjs as the single source
  of truth for runtime-aware tier resolution. core.cjs and bin/install.js
  both consume it — no duplicated lookup logic between the two files.
- F14: Added regression tests for findings #1, #2, #3, #4, #6, #10, #13
  in tests/issue-2517-runtime-aware-profiles.test.cjs. Each must-fix
  path has a corresponding test that fails against the pre-fix code
  and passes against the post-fix code.
- F15: docs/CONFIGURATION.md `model_profile` row cross-references
  #1713 / #1806 next to the `adaptive` enum value.
- F16: RUNTIME_PROFILE_MAP remains in core.cjs as the single source of
  truth; install.js imports it through the exported resolveTierEntry
  helper rather than carrying its own copy. Doc files (CONFIGURATION.md,
  USER-GUIDE.md, settings.md) intentionally still embed the IDs as text
  — code comment in core.cjs flags that those doc files must be updated
  whenever the constant changes.

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

---------

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

docs/USER-GUIDE.md

@@ -754,6 +754,19 @@ To assign different models to different agents on a non-Claude runtime, add `mod
 
 The installer auto-configures `resolve_model_ids: "omit"` for Gemini CLI, OpenCode, Kilo, and Codex. If you're manually setting up a non-Claude runtime, add it to `.planning/config.json` yourself.
 
+#### Switching from Claude to Codex with one config change (#2517)
+
+If you want tiered models on Codex without writing a large `model_overrides` block, set `runtime: "codex"` and pick a profile:
+
+```json
+{
+  "runtime": "codex",
+  "model_profile": "balanced"
+}
+```
+
+GSD will resolve each agent's tier (`opus`/`sonnet`/`haiku`) to the Codex-native model and reasoning effort defined in the runtime tier map (`gpt-5.4` xhigh / `gpt-5.3-codex` medium / `gpt-5.4-mini` medium). The Codex installer embeds both `model` and `model_reasoning_effort` into each agent's TOML automatically. To override a single tier, add `model_profile_overrides.codex.<tier>`. See [Runtime-Aware Profiles](CONFIGURATION.md#runtime-aware-profiles-2517).
+
 See the [Configuration Reference](CONFIGURATION.md#non-claude-runtimes-codex-opencode-gemini-cli-kilo) for the full explanation.
 
 ### Installing for Cline