fix(sessions): keep a session's model through recovery, refuse it off claude

SessionState now carries the model a session launched with, and both
recovery constructors (mux recovery and reboot restore) pass it back, so a
recovered session relaunches on the same --model rather than the account
default. A top-level `model` sent with any other CLI is refused, since
those take their model in their own config object, and an empty string
means no per-session model, as it does for modelOverride.

CLAUDE.md now describes both routes for a Claude model. The tests pin
which of `model` and `modelOverride` reaches the launch and which the
case file, and that a model opening with a dash renders as --model's value.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -137,7 +137,7 @@ Codeman is a Claude Code session manager with web interface and autonomous Ralph
 - **Global regex `lastIndex`** — Shared `g`-flag patterns in loops must reset `lastIndex = 0` first, or use the `execPattern()` helper in `utils/regex-patterns.ts` (resets automatically)
 - **`envOverrides` flow `CLAUDE_CODE_*` / `OPENCODE_*` / `CODEX_*` / `GEMINI_*` / `GOOGLE_*` / `ANTIGRAVITY_*` / `PI_*` / `GROK_*` / `XAI_*` / `DSH_*` / `DEEPSEEK_*` env vars, plus exact-key `CLAUDE_CONFIG_DIR`** — Set via `POST /api/sessions { envOverrides }`, stored on `Session._envOverrides`, exported by `tmux-manager.buildEnvExports()` at spawn time, persisted in `SessionState.envOverrides`. **Do NOT** write these to `<case>/.claude/settings.local.json` — that's the old path and creates UI/disk drift. (`GOOGLE_*` is the deliberately-broad Vertex-AI namespace for Gemini — see Multi-CLI prefix discipline.) `CLAUDE_CONFIG_DIR` (#255, exact match via `ALLOWED_ENV_KEYS` in `schemas.ts`) points a session at a separate Claude account/config dir for per-client subscriptions; it persists to state.json (a path, not a secret; losing it on restart would silently switch accounts). ⚠️ A relocated config dir writes transcripts outside `~/.claude/projects`, so the response viewer, subagent windows, ultracode panel and Read My Mind capture go blind for that session unless the user symlinks `projects` back into the shared tree (`ln -s ~/.claude/projects <configDir>/projects`). ⚠️ It is also one of claude's `privilegedEnvKeys` (Custom Model Endpoint Profiles, since it can redirect a session's traffic same as any other injected var), so in multi-user mode setting it via `envOverrides` is admin-only, and a non-granted owner's already-persisted `CLAUDE_CONFIG_DIR` is stripped on reboot-restore — silently returning that session to the default Claude account rather than the one it was pointed at (see `session-env-clamp.ts`). → [architecture-invariants#per-session-env-overrides-exact-key-allowlist-and-claude_config_dir](docs/architecture-invariants.md#per-session-env-overrides-exact-key-allowlist-and-claude_config_dir)
 - **Effort is NOT an env var** — never carry effort as `CLAUDE_CODE_EFFORT_LEVEL`: the env var hard-locks effort and blocks in-session `/effort` switching (incl. ultracode). It flows as the dedicated `effort` payload field → `Session._effort` → `claude --effort <level>` for regular levels incl. `max` (the settings `effortLevel` key is `enum(["low","medium","high","xhigh"]).catch(undefined)` — `max` gets SILENTLY dropped there), or `claude --settings '{"ultracode":true}'` for ultracode (rejected by `--effort`). Both are soft defaults the user can override anytime. Legacy env-var entries are auto-migrated by the Session constructor and unset from tmux sessions in `applyEnvOverrides()`. See `buildEffortCliArgs()` in `session-cli-builder.ts`, tests in `test/effort-injection.test.ts`
-- **Model choice flows via `settings.local.json`, NOT `--model` or env** — the App Settings **Claude Model** picker (`claudeModel` in `settings.json`) is read by `session-ui.js` at session create (wins over the legacy 1M-Opus toggles `opusContext1m`/`opusContext1mEnabled`), sent as the `modelOverride` payload field, and `updateCaseModel()` (`hooks-config.ts`) writes/deletes the `model` key in `<case>/.claude/settings.local.json`. This is the intended exception to the envOverrides rule above: model legitimately lives in `settings.local.json` (a soft default — in-session `/model` still works); env vars do not
+- **Model choice: a persistent default in `settings.local.json`, a per-session `--model`, never env** — the App Settings **Claude Model** picker (`claudeModel` in `settings.json`) is read by `session-ui.js` at session create (wins over the legacy 1M-Opus toggles `opusContext1m`/`opusContext1mEnabled`), sent as the `modelOverride` payload field, and `updateCaseModel()` (`hooks-config.ts`) writes/deletes the `model` key in `<case>/.claude/settings.local.json`. This is the intended exception to the envOverrides rule above: model legitimately lives in `settings.local.json` (a soft default — in-session `/model` still works); env vars do not. A caller that wants one session on a model without touching the case sends `model` on `POST /api/sessions` instead: it goes out as `claude --model <id>`, writes nothing, wins over the app-wide default, and is persisted as `SessionState.model` so both recovery paths relaunch on it (`test/routes/session-routes-claude-model.test.ts`, `test/session-model-recovery.test.ts`).
 - **Multi-CLI prefix discipline** — env-var prefix is CLI-specific (`CLAUDE_CODE_*` vs `OPENCODE_*` vs `CODEX_*` vs `GEMINI_*` vs `ANTIGRAVITY_*` vs `PI_*` vs `GROK_*` vs `DSH_*`) and the `ALLOWED_ENV_PREFIXES` allowlist in `schemas.ts` enforces this; non-prefix exceptions are exact keys in `ALLOWED_ENV_KEYS` (currently only `CLAUDE_CONFIG_DIR`), never a widened prefix. Gemini additionally allowlists the **broad `GOOGLE_*`** namespace (intentional: Vertex AI auth needs `GOOGLE_CLOUD_PROJECT`/`GOOGLE_APPLICATION_CREDENTIALS`/`GOOGLE_GENAI_USE_VERTEXAI`; it is the loosest allowlist entry, affecting only the user's own spawned CLI), and Grok allowlists **`XAI_*`** for the same vendor-namespace reason (`XAI_API_KEY` is grok's documented auth var). When adding a setting, decide which CLI(s) it applies to and gate the env export accordingly. Never blanket-forward all prefixes. ⚠️ Pi is the case that proves the rule: its ~34 provider keys (`ANTHROPIC_API_KEY`, `OPENAI_API_KEY`, `HF_TOKEN`, …) share NO prefix, and the allowlist is one GLOBAL list applied by a refine with no mode context, so admitting them for pi would widen it for every mode at once — they stay out, and pi users authenticate via `/login` or the server process's own env. ⚠️ DeepSeek repeats pi's lesson exactly: a dsh `settings.yaml` can nominate ANY env var as a provider credential (`apiKeyEnv`), so only the vendor namespaces `DSH_*` (launcher inputs incl. `DSH_PERMISSION_MODE`) and `DEEPSEEK_*` (`DEEPSEEK_API_KEY`/`DEEPSEEK_BASE_URL`) are admitted; foreign provider keys authenticate from dsh's own files or the server env. Resolver design pattern: `docs/opencode-integration.md`, `docs/pi-integration.md`, `docs/grok-integration.md`, `docs/deepseek-integration.md`
 - **Zod `.optional()` rejects `null`** — accepts `undefined` only. When the frontend builds a request body with `JSON.stringify`, an explicit `null` field is preserved on the wire and fails validation with `INVALID_INPUT`. Convert `null` → `undefined` before stringifying (e.g. `field: value ?? undefined`), or declare the schema `.nullish()`. This has caused real shipped bugs twice
 - **Local-echo overlay stays on screen**: the overlay lays its wrapped lines out DOWNWARD from the prompt row, and the text has not reached the PTY yet, so the CLI never learns the prompt is long and nothing scrolls to make room. With the keyboard up only a handful of rows are visible, so a long prompt used to run off the bottom and the user typed blind. The block now grows UPWARD once it would pass the last visible row (optional `totalRows` in `RenderParams`; the line divs are opaque, so they cover transcript above), and a prompt taller than the viewport keeps its TAIL. ⚠️ Separately, `_shrinkPaddingToFit()` (mobile-handlers.js) must never shrink `main`'s padding-bottom below the MEASURED height of the fixed bars: on phones the toolbar and accessory bar are `position: fixed`, so that padding is the only thing reserving room for them, and taking it pulled the terminal's bottom row behind them. Tests: `packages/xterm-zerolag-input/test/overlay-renderer.test.ts`, `test/mobile-keyboard-bottom-padding.test.ts`.