fix(custom-model): unset injected env on clear, resume on restart, select the model for pi/omp/grok

Custom Model Endpoint Profiles (#393) let a session point its CLI at a
custom OpenAI-compatible endpoint by injecting env vars or a config file
and restarting the CLI in place. Review of the apply path found four
things, two of them destructive. This lands all four plus the smaller
items from the same review.

1. Clearing a selection did not clear it. The injected vars reach the CLI
   via `tmux setenv`, which persists at the tmux-session level and is
   inherited by `respawn-pane` (measured: `setenv FOO bar` survived two
   successive `respawn-pane -k`), so deleting the keys from the session's
   envOverrides relaunched the CLI still pointed at the old endpoint, and
   for the configDir kinds at a HOME/CODEX_HOME/GROK_HOME that had just
   been deleted. `Session.setCustomModel()` now reports the removed keys,
   queues them (`_pendingEnvUnsets`), and `RespawnPaneOptions.unsetEnvKeys`
   carries them into `applyEnvOverrides()`, which `setenv -u`s them before
   re-applying the live overrides, on the same path that already unsets
   the legacy CLAUDE_CODE_EFFORT_LEVEL. Verified on a private tmux socket
   that `setenv -u HOME` hands the next respawn the global HOME back.

2. Applying a model to a local claude session killed the pane. The
   relaunch was `claude --session-id <id>` and Claude refuses an id that
   already has a transcript, and unlike the dead-pane respawn this one
   kills a working pane first. `restartCli()` now pins the live
   conversation id as the resume id for that respawn when the CLI's launch
   declares a `fallback` chain, which renders the same
   `--resume <id> || --session-id <id>` shape the docker and remote pane
   commands use. Gated on the registry shape, not the CLI id: an entry
   whose resume id is minted by the CLI itself never declares that chain.

3. pi, omp and grok wrote their config file and then launched without the
   `--model` that selects it, so the file was ignored. The registry entry
   now declares `customModelInjection.launchModel` (`custom/{modelId}` for
   pi and omp, grok's `[model.codeman-custom]` block name), the builder
   renders it, and `_withCustomModelLaunchModel()` applies it onto the
   respawn options through `legacyConfigField`, leaving the stored
   <Mode>Config untouched so a clear falls back to the user's own model.
   A model id the CLI's `model` token pattern cannot carry is refused
   with a 400 rather than silently dropped by the argv engine.

4. Remote (SSH) and Docker sessions reported `restarted: true` and changed
   nothing: their `restartCli()` reattaches the durable tmux rather than
   relaunching the agent, and the env lands on the local pane. Both are
   refused with a 400 until those paths are plumbed.

Smaller items from the same review:

- The selection survives a Codeman restart as the disk-only `__customModel`
  bookkeeping (endpoint, model, injected key NAMES, config dir, launch
  model; never the values, which carry the API key). Recovery re-derives
  the values from the endpoint store through the same apply path the route
  uses and keeps the bookkeeping even when the endpoint is gone, so a
  later clear still has keys to unset.
- Discovery goes through `webviewFetch()`, so the RESOLVED address is
  judged by the same egress guard the web-tab proxy uses, and `baseUrl`
  reuses `webviewUrlSchema` (http(s) only, no embedded credentials,
  link-local and cloud-metadata addresses refused). undici's `fetch failed`
  wrapper is unwrapped so the user sees the ECONNREFUSED underneath.
- `custom-model-hosts.json` is written 0600 via tmp+rename, the per-session
  config dir 0700/0600 (pi and omp embed the key literally), and that dir
  is removed with the session.
- `PR.md` is gone from the repo root and the design doc moved to
  `docs/custom-model-endpoints-plan.md` with the LAN address and the
  personal name scrubbed; every reference follows. The guide's `authStyle`
  text matches the shipped schema (`bearer | api-key`, default `bearer`)
  and says that `customModelEndpointsEnabled` is read by nothing until
  the picker lands.
- `config/tsconfig.scripts.json` typechecks `scripts/test-local-llm-harnesses.ts`
  (four real type errors fixed). It is not yet wired into `npm run typecheck`
  because that line differs on master; adding `&& tsc -p config/tsconfig.scripts.json`
  there is the one-line follow-up.

Tests: `test/session-custom-model-restart.test.ts` drives a real Session and
fails on the unfixed code for items 1 to 3; the route suite covers item 4
and the pattern refusal; `test/tmux-manager.test.ts` pins that the unsets
run before the overrides and that a shell-metachar key never reaches tmux.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

src/config/cli-registry/stock.ts

@@ -228,7 +228,7 @@ const CLAUDE: CliEntry = {
     privilegedParams: [],
     // ANTHROPIC_* is NOT in allowedPrefixes/allowedKeys above (deliberately — see the
     // allowedPrefixes comment nearby), so these are unreachable via plain envOverrides
-    // today; listed here only so the dedicated custom-model route (deployment_plan.md
+    // today; listed here only so the dedicated custom-model route (docs/custom-model-endpoints-plan.md
     // chunk 5) clamps them for a non-granted multi-user owner the same way every other
     // CLI's injection vars are clamped, the day that route widens who can set them.
     privilegedEnvKeys: [
@@ -239,7 +239,7 @@ const CLAUDE: CliEntry = {
       'ANTHROPIC_DEFAULT_OPUS_MODEL',
     ],
     gates: { nameFlag: { minVersion: '2.1.224', failClosed: true } },
-    // Custom Model Endpoint Profiles (deployment_plan.md) — verified by hand against a real
+    // Custom Model Endpoint Profiles (docs/custom-model-endpoints-plan.md) — verified by hand against a real
     // llama.cpp server. Claude reads these at process start only, so switching requires a
     // respawn, never a live hot-swap.
     customModelInjection: {
@@ -781,6 +781,10 @@ const PI: CliEntry = {
       dirEnvVar: 'HOME',
       fileName: '.pi/agent/models.json',
       template: 'pi-models-json',
+      // Writing models.json is not enough: without `--model custom/<id>` pi stays on its
+      // own default provider and fails with "No API key found for the selected model"
+      // (confirmed live). `custom` is the provider name pi-models-json declares.
+      launchModel: 'custom/{modelId}',
     },
     // HOME is not `PI_`-prefixed, so unlike the old (wrong) PI_CONFIG_DIR guess this was
     // never reachable via the generic envOverrides allowlist at all — listed here anyway,
@@ -895,6 +899,10 @@ const GROK: CliEntry = {
       dirEnvVar: 'GROK_HOME',
       fileName: 'config.toml',
       template: 'grok-toml',
+      // The `[model.<name>]` block the grok-toml template writes; `--model <name>` is what
+      // selects it (GROK_CUSTOM_MODEL_NAME in custom-model-injection.ts, pinned equal by
+      // test/custom-model-injection.test.ts so the two cannot drift).
+      launchModel: 'codeman-custom',
     },
     // GROK_HOME already matches the GROK_ allowedPrefix above, so it was ALREADY
     // reachable via plain envOverrides before this feature existed — same reasoning
@@ -1189,6 +1197,9 @@ const OMP: CliEntry = {
       dirEnvVar: 'HOME',
       fileName: '.omp/agent/models.yml',
       template: 'omp-models-yml',
+      // Same as pi: omp's own default model has no credential, so without an explicit
+      // `--model custom/<id>` it never reaches the injected provider at all.
+      launchModel: 'custom/{modelId}',
     },
   },
   overlays: {