Fix custom Claude-compatible backend isolation and execution-location popover crash

[morluto]

Summary

This fixes two Agent Mode issues found while validating a custom Claude-compatible backend configured with DeepSeek model mappings:

• Custom Claude-compatible backend launches could inherit user global/local Claude settings, including model defaults in files such as ~/.claude/settings.json or project-local Claude config. That could cause Claude Code to initialize with a user-configured model instead of the model selected by RepoPrompt.
• The execution-location / “Work locally” popover could crash while SwiftUI/AppKit resized the popover after async worktree loading.

No linked issue.

What changed

Custom Claude-compatible backend isolation

• Launch non-standard Claude-compatible backends with --bare and --setting-sources project,local.
• Propagate the resolved backend model into native/headless Claude-compatible launches.
• Set Claude slot model env vars consistently for custom backend slot mappings.
• Avoid treating ANTHROPIC_MODEL-only changes as requiring native process restart.
• Suppress effort env when a compatible backend indicates effort settings are unsupported.
• Surface Claude Code system/api_retry events as task_progress so provider throttling is visible instead of a blank Thinking… state.

Execution-location popover crash

• Keep the existing-worktree picker area fixed-height across loading/empty/loaded states.
• This avoids the AppKit/SwiftUI NSPopover animated resize path that matched the crash stack.
• Add an opt-in live UI smoke:

./conductor smoke --launch --execution-location-ui

Root cause

The custom backend configuration itself was valid. RepoPrompt passed the expected custom backend environment, but Claude Code also applied user global/local Claude settings, including model defaults in files such as ~/.claude/settings.json or project-local Claude config. Many users customize those settings for their normal Claude Code workflow. When those settings point at a different provider/model, they can override or conflict with RepoPrompt’s selected custom backend model, causing Claude Code to initialize with the user-configured model rather than the selected DeepSeek model.

--bare alone was not sufficient because Claude Code could still apply user settings env/model defaults. Adding --setting-sources project,local prevents user-level Claude settings from overriding RepoPrompt’s explicit custom backend launch environment.

The popover crash matched AppKit/SwiftUI popover layout/resize frames, including NSPopover _setContentView:size:canAnimate: and PopoverHostingView.updateAnimatedWindowSize. The popover content changed height when existing worktrees loaded asynchronously, so this removes that resize trigger.

Validation

• make dev-format
• make dev-lint
• make dev-swift-build PRODUCT=RepoPrompt
• make dev-test FILTER=ClaudeNativeIdentityPreambleTests
• make dev-test FILTER=ClaudeNativeApprovalAndResumeTests
• make dev-test FILTER=testClaudeControllerLaunchSettingsIdentityIgnoresLiveModelAndEffort
• make dev-provider-test FILTER=ClaudeCompatibleRuntimeSupportTests
• pytest Scripts/test_conductor_lifecycle.py -q
• bash -n Scripts/smoke_agent_execution_location_popover.sh

Live validation:

• A custom Claude-compatible backend configured with DeepSeek model mappings completed a smoke run successfully.
• Raw event logging confirmed the spawned Claude Code args included --setting-sources project,local and the init model was the selected DeepSeek model, not the globally configured Claude settings model.

Review notes

This PR is split into three commits:

1. fix(agent-mode): isolate Claude-compatible backend launches
2. test(agent-mode): smoke execution-location popover
3. fix(agent-mode): address custom backend review feedback

Reviewing commit-by-commit is recommended.