Reject duplicate same-app install and update requests

[kitsuyui]

Summary

• reject duplicate install or update requests for the same app before they overwrite the queued task slot
• surface ignored duplicate requests with a warning snackbar and an IPC observation event
• add regression coverage for duplicate requests that arrive while the first task is queued or already running

Why

Repeated requests for the same app reused a single mutable taskMap[id] slot. A later request could replace the queued closure for an earlier request, and the earlier queued slot would then execute the wrong closure or no-op after cleanup. This change makes the second request explicit instead of silently dropping it.

Impact

Users now keep the original in-flight request and receive immediate feedback when they try to enqueue the same app again. Queue ordering stays predictable because same-app duplicates no longer overwrite the pending task entry.

Verification

• ./node_modules/.bin/biome check main-src/libs/ipc/listener-handlers.ts main-src/libs/ipc/listener-handlers.test.ts
• ./node_modules/.bin/vitest run main-src/libs/ipc/listener-handlers.test.ts

[github-actions]

gh-counter

PR gate

	Removed	Added	+/-
TODO/FIXME	0	0	0
Type escape	0	0	0
Lint suppression	0	0	0
Electron webPreferences risk	0	0	0

Repo dashboard

	main (acd0f79)	#95 (d828146)	+/-
TODO/FIXME	0	0	0
Type escape	1	1	0
Lint suppression	30	30	0
Electron webPreferences risk	0	0	0

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Reported by gh-counter

[github-actions]

Code Metrics Report

	main (acd0f79)	#95 (d828146)	+/-
Coverage	46.6%	47.0%	+0.3%
Code to Test Ratio	1:0.3	1:0.3	+0.0
Test Execution Time	7s	5s	-2s

Details

  |                     | main (acd0f79) | #95 (d828146) |  +/-  |
  |---------------------|----------------|---------------|-------|
+ | Coverage            |          46.6% |         47.0% | +0.3% |
  |   Files             |            151 |           151 |     0 |
  |   Lines             |           2677 |          2695 |   +18 |
+ |   Covered           |           1250 |          1268 |   +18 |
+ | Code to Test Ratio  |          1:0.3 |         1:0.3 |  +0.0 |
  |   Code              |          14484 |         14651 |  +167 |
+ |   Test              |           4896 |          5011 |  +115 |
+ | Test Execution Time |             7s |            5s |   -2s |

Code coverage of files in pull request scope (100.0% → 100.0%)

Files	Coverage	+/-	Status
main-src/libs/ipc/listener-handlers.ts	100.0%	0.0%	modified

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Reported by octocov