feat: switch a running session model mid-conversation via a model-alias keyword by Koha101 · Pull Request #114 · sf8193/hydra

Koha101 · 2026-07-10T09:00:11Z

What

A thread-scoped keyword to switch a running session's model mid-conversation, without a respawn:

model sonnet
model opus

It sits alongside listen / pause / ! as a thread-scoped session command.

How

New MODEL_SWITCH_RE (^model\s+(<alias>)$), built from the existing MODEL_ALIAS_PATTERN.
In the thread-command block it resolves the alias with the existing resolveModelAlias, then sends Claude Code's own /model <id> into the session's tmux pane — Escape (clear the composer) → the command text literally via send-keys -l → Enter — the same pane-driving approach the ! interrupt already uses. Then it reacts 🔁.
/commands help text updated.

Reuses existing machinery (MODEL_ALIASES, the tmux send-keys pattern); no new dependencies.

Scope / notes

Thread-scoped, mirroring listen / pause / ! (acts on the session mapped to the thread).
Switches the live model; a restart/respawn reverts to the session's spawn model (consistent with how /model behaves in Claude Code).
Aliases are the existing set (sonnet, opus, haiku, fable, …), consistent with spawn sonnet: ….

Test

bun test daemon/__tests__/router-commands.test.ts → 40/40; bun build daemon.ts clean.

🤖 Generated with Claude Code

sf8193 · 2026-07-10T09:05:20Z

+            try {
+              Bun.spawn(['tmux', 'send-keys', '-t', info.tmuxName, 'Escape'], spawnOpts)
+              Bun.spawn(['tmux', 'send-keys', '-t', info.tmuxName, '-l', `/model ${resolved}`], spawnOpts)
+              Bun.spawn(['tmux', 'send-keys', '-t', info.tmuxName, 'Enter'], spawnOpts)


Should-fix (flagged by both reviewers): Three Bun.spawn calls fire without awaiting — no sequencing guarantee. Under OS scheduling skew, Enter can arrive before the /model text, or the text before Escape clears the composer. The existing ! handler only spawns once so it doesn't have this problem.

Fix: await each process's .exited before starting the next:

await Bun.spawn([...Escape...], spawnOpts).exited await Bun.spawn([...model text...], spawnOpts).exited await Bun.spawn([...Enter...], spawnOpts).exited

sf8193 · 2026-07-10T09:05:20Z

+            } catch (err) {
+              process.stderr.write(`daemon: model switch failed for ${info.tmuxName}: ${err instanceof Error ? err.message : err}\n`)
+            }
+            void gateway.react(msg.channelId, msg.id, '🔁').catch(() => {})


Should-fix (flagged by both reviewers): The 🔁 react fires unconditionally — even when all three tmux spawns silently fail (stale pane, dead session). The user gets false confirmation that the switch happened.

Move the react inside the try block after the spawns, or better yet, await .exited (per the sequencing comment) and check exit codes before reacting. On failure, reply with an error message instead of reacting.

sf8193 · 2026-07-10T09:05:20Z

+          // approach as the ! interrupt below.
+          const modelMatch = msg.content.match(MODEL_SWITCH_RE)
+          if (modelMatch) {
+            const resolved = resolveModelAlias(modelMatch[1]) ?? modelMatch[1]


Should-fix (flagged by both reviewers): When resolveModelAlias returns undefined (typo like "sonett"), the raw string is silently injected into the tmux pane via /model sonett. Claude Code will reject it, but the user gets no feedback — just a 🔁 react suggesting success.

Other spawn/review commands in this file only proceed when resolution succeeds. Match that pattern: reply with an unknown-alias error and return early when resolveModelAlias returns undefined.

sf8193 · 2026-07-10T09:05:20Z

 const SPAWN_WT_MODEL_RE = new RegExp(`^(?:spawn-wt|/spawn-wt)\\s+(${MODEL_ALIAS_PATTERN}):\\s*(\\S+)\\s+([\\s\\S]+)`, 'i')
 const BARE_ALIAS_RE = new RegExp(`^(${MODEL_ALIAS_PATTERN}):?$`, 'i')
+// "model sonnet" / "model opus" — switch a running session's model mid-conversation
+const MODEL_SWITCH_RE = new RegExp(`^model\\s+(${MODEL_ALIAS_PATTERN})\\s*$`, 'i')


Nit (flagged by both reviewers): 'model' is not added to COMMAND_PREFIXES (used by COMMAND_RE at line ~28). Every other named command (usage, kill, restart, etc.) has a prefix entry. Without it, a non-allowlisted sender who types model sonnet won't trigger the warning log — the message falls through silently.

sf8193 · 2026-07-10T09:05:20Z

+          const modelMatch = msg.content.match(MODEL_SWITCH_RE)
+          if (modelMatch) {
+            const resolved = resolveModelAlias(modelMatch[1]) ?? modelMatch[1]
+            const spawnOpts = { stdio: ['pipe', 'pipe', 'pipe'] as const }


Nit: stdio: ['pipe', 'pipe', 'pipe'] creates pipes that are never read. If tmux send-keys writes to stderr on error (e.g., unknown pane), the pipe buffer fills with no reader. Since the output isn't consumed, stdio: ['ignore', 'ignore', 'ignore'] (or 'inherit' to surface errors in daemon logs) is more appropriate.

Koha101 · 2026-07-10T09:24:52Z

Thanks for the thorough review — addressed all four should-fixes and pushed an update:

Sequencing (Reliable Slack bridge: spawned-session fixes, rich Markdown, onboarding #1): each send-keys now awaits its .exited before the next, so Escape → /model … → Enter can't arrive out of order.
React only on success (Session lifecycle, command vocabulary, platform abstraction, and resilience #2): the 🔁 now fires only if all three spawns exit 0; on failure it replies with an error instead of a false confirmation.
Unknown alias (feat: push-based attachment delivery #3): broadened the match to any single token and validate via resolveModelAlias — a typo now gets an "unknown alias" reply (with the known list), matching the spawn/review commands. Minor note for the record: the original MODEL_SWITCH_RE was built from MODEL_ALIAS_PATTERN, so model sonett never actually matched and never reached /model — but explicit feedback is the nicer behavior regardless, so this is a good change either way.
stdio (refactor: DRY notification payload builder #5): switched to ['ignore','ignore','ignore'] — and it matters a bit more now that the spawns are awaited (unread pipes could otherwise stall on a full buffer).

On the COMMAND_PREFIXES nit (#4) — I left it out deliberately: model is a thread-scoped session command like listen / pause / !, and none of those are in COMMAND_PREFIXES either. Per the comment at the top of the file, thread commands are gated on session ownership (not allowFrom), so non-allowlisted senders can't reach them; COMMAND_PREFIXES is the main-channel command surface. Adding model alone would make it the odd one out. Happy to add it if you'd rather have it there for the unauthorized-command log — just say the word.

…as keyword Adds a thread-scoped keyword (model <alias>), matched alongside listen/pause, that switches the running session model without a respawn. It resolves the alias with the existing resolveModelAlias and sends Claude Code's own /model into the session tmux pane (Escape, the text literally via -l, then Enter) - the same pane-driving approach as the interrupt command - then reacts. Reuses MODEL_ALIASES; no new deps; help text updated. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Koha101 · 2026-07-10T10:31:09Z

Pushed one more fix (found while running this against current Claude Code): recent CC versions pop a "Switch model?" confirmation ("1. Yes / 2. No") when the switch invalidates the prompt cache. The Escape → /model <id> → Enter sequence submits the command but leaves the pane parked on that modal, so the session stops responding until someone answers it.

Fix: after the switch keystrokes, wait a beat (~800ms) and send one more Enter to confirm the highlighted default (Yes). If no confirmation appears, the extra Enter lands on an empty composer and is a harmless no-op.

bun build daemon.ts clean; router-commands 40/40.

sf8193 · 2026-07-10T12:06:34Z

+// "model sonnet" / "model opus" — switch a running session's model mid-conversation.
+// Matches any single token so a typo'd alias gets a clear error instead of silently
+// falling through; the alias is validated (resolveModelAlias) at the call site.
+const MODEL_SWITCH_RE = /^model\s+(\S+)\s*$/i


Should-fix (bump, escalated from prior nit — flagged by sp-reviewer): 'model' is still not in COMMAND_PREFIXES. Previous review noted this means the warning log is skipped for non-allowlisted senders. Escalating because model mutates the session runtime (cost, capability, cache invalidation) — unlike the other thread-scoped commands that skip the gate (listen/pause, which are harmless visibility toggles). Any user who can post in the thread can switch the model with no ownership check.

Minimal fix: add 'model' to COMMAND_PREFIXES. Better: also gate on msg.authorId matching the session creator or allowFrom.

…193#114 review) Round-2 review fixes: - Gate `model <alias>` on allowFrom — it mutates session cost/capability, unlike the harmless listen/pause toggles it sits beside. Not a COMMAND_PREFIXES entry (those are global commands; this is thread-scoped). - Replace the blind 800ms sleep before the "Switch model?" confirm with a pane poll (capturePane, up to ~3s) that fires Enter only once the modal is seen — a slow modal no longer swallows a timed Enter. - Confirm is best-effort: a capture error leaves the submitted switch intact; only a seen-but-unconfirmed modal (pane parked) reports failure, so a transient capture hiccup can't falsely report a delivered switch as failed. - Extract capturePane into util.ts (shared with getContextPercent), single-quote-escaping the pane name. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

sf8193 · 2026-07-10T15:07:43Z

+              // Claude Code shows "Switch model?" only when the switch invalidates the cache.
+              // Poll for it rather than blind-firing a timed Enter (a slow modal would swallow
+              // one); best-effort — a capture error leaves the submitted switch intact, only a
+              // seen-but-unconfirmed modal (pane parked) downgrades success to failure.


Nit (flagged by both reviewers): The poll constants 12 and 250 (3 s ceiling) are magic numbers. A named pair would make the timeout tunable and self-documenting:

const CONFIRM_POLL_MS = 250 const CONFIRM_POLL_MAX = 12 // 3 s ceiling

Minor — the inline comment already explains the mechanism, so this is cosmetic.

sf8193 · 2026-07-10T15:12:37Z

+          const modelMatch = msg.content.match(MODEL_SWITCH_RE)
+          if (modelMatch) {
+            if (!isAllowed) {
+              process.stderr.write(`daemon: model switch from non-allowlisted sender ${senderId} on ${info.tmuxName} ignored\n`)
+              return
+            }
+            const resolved = resolveModelAlias(modelMatch[1])
+            if (!resolved) {
+              void reportError(msg.channelId, msg.id, 'model', `unknown model alias "${modelMatch[1]}"`, `Known aliases: ${Object.keys(MODEL_ALIASES).join(', ')}`)
+              return
+            }
+            const spawnOpts = { stdio: ['ignore', 'ignore', 'ignore'] as const }
+            let switched = true
+            try {
+              for (const keys of [['Escape'], ['-l', `/model ${resolved}`], ['Enter']]) {
+                if ((await Bun.spawn(['tmux', 'send-keys', '-t', info.tmuxName, ...keys], spawnOpts).exited) !== 0) {
+                  switched = false
+                  break
+                }
+              }
+            } catch (err) {
+              switched = false
+              process.stderr.write(`daemon: model switch failed for ${info.tmuxName}: ${err instanceof Error ? err.message : err}\n`)
+            }
+            if (switched) {
+              // Claude Code shows "Switch model?" only when the switch invalidates the cache.
+              // Poll for it rather than blind-firing a timed Enter (a slow modal would swallow
+              // one); best-effort — a capture error leaves the submitted switch intact, only a
+              // seen-but-unconfirmed modal (pane parked) downgrades success to failure.
+              try {
+                for (let i = 0; i < 12; i++) {
+                  await new Promise(r => setTimeout(r, 250))
+                  if (/Switch model\?/i.test(capturePane(info.tmuxName))) {
+                    if ((await Bun.spawn(['tmux', 'send-keys', '-t', info.tmuxName, 'Enter'], spawnOpts).exited) !== 0) switched = false
+                    break
+                  }
+                }
+              } catch (err) {
+                process.stderr.write(`daemon: model switch confirm-check failed for ${info.tmuxName}: ${err instanceof Error ? err.message : err}\n`)
+              }
+            }
+            if (switched) {
+              process.stderr.write(`daemon: model switch -> ${resolved} for ${info.tmuxName}\n`)
+              void gateway.react(msg.channelId, msg.id, '🔁').catch(() => {})
+            } else {
+              void reportError(msg.channelId, msg.id, 'model', `couldn't switch model on ${info.tmuxName}`, 'The pane may be gone or stuck on the confirmation.')
+            }
+            return
+          }
+


can you put all of this in helper function? similar to above with like

if (cancelDesignMatch) { void handleCancelDesignIntercept(msg) return }

… poll constants (sf8193#114 review) Author review follow-ups (PR approved): - Move the inline `model <alias>` block out of router.ts into handleModelSwitchIntercept in commands/thread.ts, matching the sibling intercept handlers (fork/resume/respawn) — router call site is now the same `void handle...Intercept(msg, ...); return` shape as its neighbors. - Name the confirm-poll magic numbers: CONFIRM_POLL_MS / CONFIRM_POLL_MAX (~3s ceiling). Behavior-preserving: the helper self-resolves the session via resolveThreadSessionFromMsg (same thread-id resolution as the router's getByThread), and the allowFrom gate still fires before any pane action. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

sf8193 · 2026-08-17T18:14:17Z

+          break
+        }
+      }
+    } catch (err) {


Should-fix (flagged by both reviewers): The catch block logs the error but doesn't set switched = false. If the pane dies during polling (capturePane throws), switched stays true and the user gets a false 🔁 success reaction.

} catch (err) { switched = false // ← add this process.stderr.write(`daemon: model switch confirm-check failed for ${info.tmuxName}: ${err instanceof Error ? err.message : err}\n`) }

The comment says "a capture error leaves the submitted switch intact" — but a dead pane means the switch didn't land, so the react should not fire.

sf8193 · 2026-08-17T18:14:17Z

+export function capturePane(tmuxName: string): string {
+  const name = tmuxName.replace(/'/g, "'\\''")
+  return execSync(`tmux capture-pane -t '${name}' -p 2>/dev/null`, { stdio: ['pipe', 'pipe', 'pipe'], timeout: 2000 }).toString()
+}


Nit (ts-reviewer): capturePane uses execSync with shell string interpolation. The single-quote escaping is adequate, but execFileSync('tmux', ['capture-pane', '-t', tmuxName, '-p'], ...) would avoid the shell entirely and match the tmuxHasSession pattern directly above. The 2>/dev/null redirect is also redundant when stderr is already piped via stdio.

sf8193 reviewed Jul 10, 2026

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Koha101 force-pushed the feat/model-switch branch from cf930c9 to 65349e0 Compare July 10, 2026 09:20

Koha101 marked this pull request as ready for review July 10, 2026 09:24

Koha101 force-pushed the feat/model-switch branch from 65349e0 to e4bd0f6 Compare July 10, 2026 10:30

sf8193 reviewed Jul 10, 2026

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sf8193 approved these changes Jul 10, 2026

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sf8193 force-pushed the main branch from 083a8f9 to 393229d Compare July 12, 2026 06:07

sf8193 reviewed Aug 17, 2026

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feat: switch a running session model mid-conversation via a model-alias keyword - #114

feat: switch a running session model mid-conversation via a model-alias keyword#114
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Koha101 commented Jul 10, 2026

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