fix: fire on-enter for the default route at startup (#81)

[geoffjay]

Summary

Fixes #81. A <route>'s on-enter hook did not fire for the default route when a <router> first mounted at startup — it only fired on subsequent navigations, making on-enter unusable for "run something when the initial page is shown."

Root cause: the initial path is seeded through lazy initialization (router_current_path, called from the render pass) without a path change, so apply_one_navigation — which fires on-leave/on-enter only when old_path != new_path — never sees the initial mount and skips its on-enter.

Approach

Firing from the render pass directly would risk a re-entrant deadlock (call_handler holds the extension_manager write lock), so this mirrors the existing deferred-navigation design:

• Added a pending_initial_enters queue on NemoRuntime.
• When router_current_path first seeds a router to its default (or --route override), it enqueues the router id and pings data_notify (once — later renders find existing state).
• New fire_pending_initial_enters() drains the queue, projects the route's path+params, and fires its on-enter once, outside the extension lock.
• The App poll loop calls it right after apply_pending_navigations() and before the data-update pass, so the projection propagates in the same wake.

Result: the default route's on-enter fires at startup, consistent with later navigations; each route's on-enter fires exactly once when it becomes active.

Testing

• New regression test test_initial_default_route_fires_on_enter (fires with no prior navigation; fires exactly once).
• Existing navigation and --route override tests still pass; clippy clean.

Docs

Updated docs/knowledgebase/patterns/routing.md and added a log.md entry.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 56.59%. Comparing base (82b766c) to head (8721f07).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #87   +/-   ##
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  Coverage   56.59%   56.59%           
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  Files          78       78           
  Lines        6866     6866           
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  Hits         3886     3886           
  Misses       2980     2980           

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