fix: improve novice error messages, gated by automated smoke

[EitanWong]

Simulated a non-technical user hitting common failures (per the 'simulate a novice' direction):\n\n- missing --join-code printed 'rdev-host foreground placeholder' (dev leftover) -> now explains what to do\n- join failures ignored gateway user_summary -> now prefer the human-readable copy\n- unreachable gateway -> plain guidance instead of route-pool jargon\n\nux-smoke now asserts all five error paths stay readable, so regressions fail CI.

Summary by CodeRabbit

• Bug Fixes

  • Improved error messages for failed session joins, including clearer operator-facing details.
  • Added actionable guidance when no healthy gateway routes are available.
  • The serve command now clearly reports when a join code is missing instead of displaying misleading status output.
  • Improved handling and messaging for invalid join codes, unreachable gateways, and port conflicts.

• Tests

  • Expanded smoke-test coverage for common command and connection error scenarios.

[coderabbitai]

📝 Walkthrough

Walkthrough

The CLI now reports actionable guidance for missing or invalid join codes, unreachable gateways, unavailable routes, unknown commands, and port conflicts. UX smoke tests cover these error paths.

Changes

CLI Error Guidance

Layer / File(s)	Summary
Error messages and smoke coverage internal/hostcmd/exitcode.go, internal/hostcmd/hostcmd.go, internal/hostcmd/route_pool.go, scripts/ux-smoke.sh	Join failures prefer UserSummary and fall back to Message. Missing join codes now return usage guidance. No-healthy-route errors include gateway and network guidance. UX smoke tests cover the updated error paths.

Estimated code review effort: 2 (Simple) | ~10 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main change: improving novice-facing error messages and adding automated smoke coverage.

✨ Finishing Touches 💡 1

🛠️ Fix failing CI checks 💡

• Create stacked PR
• Commit on current branch

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/40-novice-error-paths

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[coderabbitai]

🧹 Nitpick comments (1)

scripts/ux-smoke.sh (1)

162-166: 🎯 Functional Correctness | 🔵 Trivial | ⚡ Quick win

Assert the gateway user_summary, not a generic keyword.

Line 163 accepts any output containing invalid or no longer active. The terse protocol message can contain the same text, so this test passes even if NewJoinSessionResponseError stops selecting UserSummary. Configure distinct message and user_summary values in the fixture, then assert the exact user_summary.

Suggested assertion shape

- if [[ "$OUT" =~ invalid|no\ longer\ active ]]; then
+ if [[ "$OUT" == *"$EXPECTED_USER_SUMMARY"* ]] &&
+    [[ "$OUT" != *"$EXPECTED_PROTOCOL_MESSAGE"* ]]; then

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@scripts/ux-smoke.sh` around lines 162 - 166, Update the bad join-code fixture
and assertion in the smoke test around the rdev-host serve invocation: configure
distinct protocol message and gateway user_summary values, then assert the exact
user_summary instead of matching generic “invalid” or “no longer active”
keywords. Keep the failure diagnostic output for unexpected responses.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@scripts/ux-smoke.sh`:
- Around line 162-166: Update the bad join-code fixture and assertion in the
smoke test around the rdev-host serve invocation: configure distinct protocol
message and gateway user_summary values, then assert the exact user_summary
instead of matching generic “invalid” or “no longer active” keywords. Keep the
failure diagnostic output for unexpected responses.

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: f0c8823b-a07f-4b8d-9a72-e8a70c135eea

📥 Commits

Reviewing files that changed from the base of the PR and between 5398c23 and b3bb543.

📒 Files selected for processing (4)

• internal/hostcmd/exitcode.go
• internal/hostcmd/hostcmd.go
• internal/hostcmd/route_pool.go
• scripts/ux-smoke.sh