fix: close_tab() recovers session state when closing the currently attached tab

[mvanhorn]

Summary

close_tab() now switches the harness to a surviving real tab (or a fresh about:blank) before closing the currently attached tab, so the daemon session never points at a dead target.

Why this matters

Before this change, the no-arg form of close_tab() issued Target.closeTarget against the attached targetId without updating the daemon session that switch_tab() previously registered. After close_tab() the daemon still believed the now-dead targetId/sessionId was active, so the next call into js(), page_info(), current_tab(), or _mark_tab() landed on a dead session and failed until the caller manually switch_tab()'d.

Repro:

new_tab("https://example.com")
close_tab()
page_info()  # fails: not attached to live tab

Maintainer @sauravpanda filed #379 with a clear cause + Option (a) fix sketch.

Changes

• close_tab(target=None) now detects whether the target equals the currently attached tab. If so, it picks a surviving real tab via list_tabs(include_chrome=False) and switch_tab()s to it before closing; if no other real tab exists, it opens a fresh about:blank first. The fast path for explicit non-current targets is unchanged.
• Error path: if Target.closeTarget fails after the switch, the original session is restored rather than left half-migrated.

Testing

pytest tests/unit/test_helpers.py — 22/22 pass. Added 4 new test cases:

• Happy path: two tabs, no-arg close, current tab + daemon session land on the survivor.
• Single-tab fallback: about:blank created, session points at it, page_info() succeeds.
• Explicit non-current close: current tab + session unchanged.
• Error path: simulated close failure restores original session intact.

Fixes #379

---

Summary by cubic

Fixes a bug where closing the currently attached tab left the session pointing at a dead target. Now close_tab() switches to a live tab (or creates about:blank) before closing so follow-up calls work. Fixes #379.

• Bug Fixes
  • When closing the current tab, switch to a surviving real tab first; if none, open about:blank.
  • If closing a non-current tab, leave the current session unchanged.
  • If close fails after switching, restore the original session.
  • Added unit tests covering survivor switch, blank fallback, non-current close, and failure rollback.

^{Written for commit d0f0807. Summary will update on new commits. Review in cubic}

[cubic-dev-ai]

1 issue found across 2 files

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="src/browser_harness/helpers.py">

<violation number="1" location="src/browser_harness/helpers.py:352">
P2: close_tab() leaks a fallback about:blank tab when Target.closeTarget fails in single-tab mode</violation>
</file>

<sub>Reply with feedback, questions, or to request a fix.

Fix all with cubic | Re-trigger cubic</sub>

[cubic-dev-ai]

P2: close_tab() leaks a fallback about:blank tab when Target.closeTarget fails in single-tab mode

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At src/browser_harness/helpers.py, line 352:

<comment>close_tab() leaks a fallback about:blank tab when Target.closeTarget fails in single-tab mode</comment>

<file context>
@@ -326,11 +326,35 @@ def new_tab(url="about:blank"):
+    if other_tabs:
+        switch_tab(other_tabs[0])
+    else:
+        new_tab()
+    try:
+        cdp("Target.closeTarget", targetId=target_id)
</file context>