A user running roughly 150 warm terminals in Influxx reported something specific and reproducible: every time they switched back to a workspace, the first few keystrokes just didn't show up. Not a crash, not an error — a near-one-second freeze that made the terminal feel like it was thinking about whether to accept input at all. The bug turned out to live inside a single daemon RPC called listSessions, and finding it meant ruling out almost everything else first.
The Symptom: A Warm Switch That Stalls Typing for Nearly a Second
Influxx keeps agent terminals alive in a background daemon so that switching tabs, closing a window, or even restarting the app doesn't kill a running Claude Code or Codex session. The tradeoff is that the renderer and the daemon are separate processes talking over IPC, and every tab switch has to reconcile what the UI thinks is true with what the daemon actually has running. For most users, with a handful of terminals open, that reconciliation is invisible. For a user who had built up around 150 live daemon terminals across long-running projects, it was not invisible at all — it was an 800ms-to-1.8-second stall on the very first keystroke after switching back to a workspace.
The bug report didn't mention a specific RPC name or a specific function. It just described the symptom: switch tabs, type, wait, then watch the buffered keystrokes land all at once. That's the kind of report that could plausibly point to a dozen different subsystems — and the investigation had to work through most of them before it found the real one.
Ruling Out Focus, Rendering, and PTY Readiness
Focus and Paint Were Not the Problem
The first instinct with any "typing feels broken after switching tabs" report is to suspect focus handling — maybe the input element wasn't actually receiving keyboard events, or a re-render was stealing focus mid-transition. That was ruled out with direct measurement rather than assumption: focus state and paint timing were checked independently of the input pipeline, and neither showed anything close to the delay users were reporting. The freeze wasn't cosmetic and it wasn't a focus race.
Shell and PTY Startup Were Not the Problem Either
The second suspect was PTY readiness — the idea that a shell process attached to a long-idle terminal might need to "wake up" before it could accept input again, especially at the scale of 150 concurrent sessions. This was also ruled out with its own control measurement, isolating shell and PTY startup time from everything downstream of it. The PTYs were already alive and ready; nothing about the shell process itself explained a delay measured in hundreds of milliseconds.
Ruling both of these out mattered because they pointed the investigation somewhere less obvious: not the terminal itself, and not the rendering layer, but whatever code path runs the moment a hidden terminal tab becomes visible again.
Building a Direct Line Into the Daemon
Once focus, paint, and PTY readiness were off the table, the remaining suspect was the daemon event loop itself — but proving that meant separating "the daemon is slow" from "the app is slow talking to the daemon." The investigation built a purpose-specific throwaway-terminal test harness capable of spinning up large numbers of live daemon sessions on demand, plus a direct daemon-socket client that could issue RPCs to the daemon without going through the Influxx app UI at all.
That second piece was the one that made the difference. By talking to the daemon directly over its socket, it became possible to time individual RPCs in isolation — no renderer, no IPC bridge, no paint cycle in the way. If a call was slow, it was slow inside the daemon process itself, full stop.
"We needed a way to ask the daemon a question and get a timestamp back without the app in between, because the app was the thing everyone assumed was guilty. Once we had a socket client that could hammer the daemon directly, the slow call basically raised its hand."
— Priya Nakamura, Staff Engineer, Terminal Infrastructure at ETAPX
Inside listSessions: Serializing 137 Full Screen Buffers to Answer a Yes/No Question
The direct daemon probes pointed at one RPC: a session-listing call, internally the thing everything else calls listSessions, used by the renderer to check whether a given terminal was still alive in the daemon. Conceptually this should be a cheap lookup — is session X still in the daemon's table, yes or no. In practice, the routine looped over every live session the daemon was tracking and, for each one, serialized that session's full snapshot just to read its column and row dimensions off of it.
The snapshot call it was reusing wasn't built for a liveness check — it serializes the complete headless terminal buffer, scrollback and all, because that's what a real snapshot consumer (like restoring a terminal's visible contents) actually needs. Using it to answer "is this alive, and what size is it" meant a routine, frequent, supposedly-cheap check scaled with the total scrollback held across every session in the daemon, not with the one terminal anyone actually cared about.
The part that turned this from a slow RPC into a felt UI freeze was where it got called from. Switching a terminal tab from hidden back to visible in the renderer triggered dead-session reconciliation — logic meant to catch the edge case where a terminal died while its tab was hidden. That reconciliation queried the entire daemon's session list rather than asking about just the one pane being revealed. So a UI action that conceptually needed to check one session ended up paying the cost of serializing all of them.
The Numbers: What 552 Milliseconds Actually Costs You
With the direct daemon-socket client in hand, the cost became easy to put a number on. Against a real profile with 137 live daemon sessions, two separate direct calls to the session-list RPC measured 552ms and 547ms — consistent, not a one-off spike. That's not just slow in isolation; the daemon runs on a single event loop, so anything that blocks it blocks everything else queued behind it too.
- 552ms and 547ms: measured wall-clock time for two back-to-back session-list calls against 137 live sessions, taken directly off the daemon socket with the app entirely out of the loop.
- Over a second, queued: a routine keep-alive ping issued right after those two calls got stuck behind them in the event loop, pushing its own completion out past the one-second mark.
- ~1.8 seconds: the average echo latency measured before the fix when a user typed into a terminal immediately after a warm switch — the visible, felt version of the same stall.
The keep-alive detail is what made this a correctness bug and not just a performance nuisance. Influxx's daemon uses lightweight pings to confirm a session is still responsive; when a genuinely cheap, latency-sensitive check gets stuck in line behind an accidentally expensive one on a single-threaded event loop, the daemon's own health-checking machinery becomes a casualty of the bug it should have been catching sooner.
"I have a lot of long-lived agent sessions going at once, so I'm switching between workspaces constantly. It got to the point where I'd switch tabs and just wait a beat before I started typing, because if I didn't, half my first sentence would get eaten and then dumped in all at once. I didn't think it was a bug at first, I thought it was just what happens when you keep too many terminals open."
— Marcus Ferreira, platform engineer at a logistics software company, Influxx user
The Fix: Ask About One Session, Not All of Them
The fix replaced the global sweep with a targeted check: does this one specific PTY exist, answered against a single provider-owned in-memory state rather than by looping the entire daemon and re-serializing every session's snapshot. The dead-session reconciliation that runs on a warm tab switch now asks exactly the question it needs to ask — about the one pane being revealed — instead of asking the daemon to account for everything it's holding.
Failing Open Instead of Failing Confident
The more interesting design decision is what happens when that targeted check can't get a clean answer. Rather than treating an ambiguous result as an authoritative "this session is dead" and hiding the pane, the reconciliation logic fails open — it keeps the pane visible. A liveness check that's wrong in the direction of hiding a terminal that's actually fine is far more disruptive than one that's wrong in the direction of briefly showing a terminal that turns out to be gone; the former looks like data loss, the latter is a self-correcting cosmetic delay.
"This is the kind of bug that only shows up once people actually trust the product enough to load it up with 150 live sessions. It's a good problem to have, but it's still a problem — a daemon that scales its cheapest, most frequent check with total scrollback across every session isn't going to hold up as usage grows, and typing latency is about as unforgiving a place as it can show up."
— Sana Okafor, VP of Engineering at ETAPX
Confirming It Stays Fixed
Because the root cause was a call graph problem — the warm-switch path reaching for a global, expensive RPC when it should have reached for a cheap, scoped one — the regression test needed to assert behavior, not just timing. The end-to-end test harness artificially stalled the old session-list call by 800ms and then asserted that the warm-switch path made zero calls to it at all. If a future change reintroduces the dependency, the test fails immediately regardless of whether the stall happens to be fast on a given machine or dataset.
That end-to-end check sits alongside over 500 passing focused unit tests covering terminal lifecycle and PTY handling more broadly, which exercise the surrounding daemon and reconciliation logic without needing hundreds of live sessions to do it. Together they cover both the specific regression and the general behavior of the systems it touched.
The measured result in the automated test artifact: post-fix echo latency on a warm-switched terminal came in at roughly 10ms, down from the roughly 1.8-second average measured before the fix. That's not a tuning improvement — it's the difference between a check that costs one lookup and a check that costs serializing 137 sessions' worth of terminal buffers.
Frequently Asked Questions
Was this bug specific to very large numbers of terminals, or would it show up with just a few?
The mechanism affects any number of daemon sessions, but the cost scales with total sessions and their scrollback, so it was only severe enough to notice at scale — the reproduction case used roughly 150 live daemon terminals with a direct measurement of 137 sessions.
Why does Influxx run terminals in a background daemon instead of inside the app process directly?
The daemon is what lets PTYs survive app restarts and window closes, so a long-running agent session in Claude Code or Codex keeps working even if the Influxx window itself is closed and reopened; the tradeoff is that the app and the daemon have to stay in sync over IPC, which is exactly where this bug lived.
What is dead-session reconciliation, and why does it run on every tab switch?
It's the logic that checks whether a terminal pane's underlying PTY is still alive in the daemon before showing it again, meant to catch the edge case of a session dying while its tab was hidden; the bug was that it queried the daemon's entire session list instead of just the one session being revealed.
How was this diagnosed without just guessing at the slow function?
By systematically ruling out candidates with dedicated control measurements — focus and paint timing, then PTY and shell startup time — before isolating the daemon itself using a direct socket client and a throwaway-terminal test harness that bypassed the app UI entirely.
Why does the fix keep the pane visible instead of hiding it when the check is unsure?
Because a false "this session is dead" reads to a user as lost work, while a false "this session is alive" just means the pane briefly shows something that gets corrected shortly after — the fix deliberately fails open rather than treating an ambiguous liveness result as authoritative.
How is this regression actually prevented from coming back?
An end-to-end test artificially stalls the old global session-list call by 800ms and asserts that the warm-switch path makes zero calls to it, backed by over 500 focused unit tests across terminal lifecycle and PTY handling.
Does this fix change what the session-list RPC itself returns, or just who calls it and when?
It's the latter — the fix is about the call graph, replacing a global sweep with a targeted single-PTY check against in-memory state for the warm-switch path; it doesn't change the underlying snapshot mechanism, which still exists for the cases that genuinely need a full buffer.
The bug was never really about typing latency — it was about a cheap-looking function name hiding an expensive operation, and about a UI event that only needed to ask one question ending up, several layers down, asking the daemon to account for everything it had.
