fix: an approval runs its stored connection action only once

[charan-rathore]

What this changes

An approval-gated connection action could be executed more than once under the same approval.

claimAction keys execution claims on (threadId, toolCallId), which stops a double click or a retried request from running twice. But nothing bound the approval itself to one run: after an approved action completed, POSTing the same approvalId with a fresh toolCallId passed every check (approval found, conversation matches, inside the one-hour TTL, tool still bound) and ran the stored request again. While the first run was still in flight, a second toolCallId could even start a concurrent execution of the same approved call.

The POST path now looks up the action an approval was already claimed for and refuses a different toolCallId with a 409. Same-toolCallId retries still recover their saved result, and this composes with the interrupted-claim reclaim in #135, which reclaims under the same toolCallId.

Tests

New regression test in tests/connections.test.ts: approve once (runs, receipt done), then POST the same approvalId under a new toolCallId and expect a 409 with the send mock called exactly once. The test failed before the change (the stored request ran a second time) and passes after. Full suite: 303 passed across 48 files, tsc --noEmit and eslint clean.

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[charan-rathore]

This is green on CI and conflict-free on my end. Is there anything you'd like changed before it can land? Happy to adjust.