fix: exorcise goroutine-leaking util.After from the codebase

[johnstcn]

Summary

• Replace all 5 util.After call sites with inline clock.NewTimer + explicit Stop()
• Delete the leaky util.After function entirely

Problem

util.After spawned a goroutine that sent on an unbuffered channel. If the caller's select picked a different branch (e.g. ctx.Done()), the goroutine blocked forever on the send — leaking one goroutine per cancellation.

Changes

• lib/screentracker/pty_conversation.go — Phase 1 stability timer + Phase 2 carriage-return timer now use inline NewTimer with Stop() on both cancel and normal paths
• lib/termexec/termexec.go — ReadScreen vsync timer + Close timeout timer replaced with inline NewTimer
• cmd/attach/attach.go — Grace period timer replaced, removed unused util import
• lib/util/util.go — Deleted After function

Implementation context

The goroutine leak was originally flagged by Copilot in PR #208. The After helper used make(chan time.Time) (unbuffered) + a goroutine doing ch <- <-timer.C. If nobody drained ch, the goroutine blocked on send forever. Inline NewTimer is the idiomatic quartz pattern already used by WaitFor itself.

Fixes #210

🤖 Written by a Coder Agent. Will be reviewed by a human.

[github-actions]

✅ Preview binaries are ready!

To test with modules: agentapi_version = "agentapi_211" or download from: https://github.com/coder/agentapi/releases/tag/agentapi_211

[johnstcn]

self-reviewed

[Copilot]

Pull request overview

This PR removes the goroutine-leaking util.After helper and replaces its usage with inline quartz.Clock.NewTimer timers that are explicitly Stop()’d, preventing goroutine leaks when a select takes a non-timer branch (e.g., ctx.Done()).

Changes:

• Deleted util.After from lib/util/util.go.
• Replaced all previous util.After call sites with clock.NewTimer(...) + Stop() patterns (including ctx-cancel paths where applicable).
• Cleaned up cmd/attach imports after removing the last util.After usage.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
lib/util/util.go	Removes the leaky After helper entirely.
lib/termexec/termexec.go	Replaces the vsync sleep and Close timeout with NewTimer and Stop().
lib/screentracker/pty_conversation.go	Replaces Phase 1 stability + Phase 2 carriage-return delays with explicit timers that are stopped on both normal and cancel paths.
cmd/attach/attach.go	Replaces grace-period wait with NewTimer and removes now-unused util import.

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