chore: make the never-mutated socket payload a let

[austinywang]

Summary

Main's full CI currently fails the Swift warning budget in tests-build-and-lag with +1 Sources/TerminalController.swift: variable 'payload' was never mutated; consider changing to 'let' constant (see https://github.com/manaflow-ai/cmux/actions/runs/34057995765 on main and the same finding on the #12137 branch). The declaration at line 8779 builds a dictionary and returns it unchanged, so this makes it a let. No budget file change.

Verification

• One-line change; full ci.yml dispatched on this branch so the Validate Swift warning budget step can confirm the count is back under budget (link in the comments).
• No user-facing strings changed.

🤖 Generated with Claude Code

https://claude.ai/code/session_01H8Eci7rC11iSuCw4F4DE2g

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Summary by cubic

Changes the payload variable in TerminalController.swift from var to let to fix the failing Swift warning budget check. The value is returned unchanged, so there's no behavior change.

^{Written for commit 8288d60. Summary will update on new commits.}

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Note

Low Risk
Single declaration change with no logic or API behavior change; only silences an unused-mutation compiler warning.

Overview
Fixes a Swift warning budget failure on main by declaring the success-path response dictionary as let instead of var in the browser keyboard replay handler inside TerminalController.swift.

When native keyboard replay delivers, the handler still returns the same workspace/surface IDs and v2 refs; nothing in that path mutates the dictionary after it is built.

^{Reviewed by Cursor Bugbot for commit 8288d60. Bugbot is set up for automated code reviews on this repo. Configure here.}

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Project	Deployment	Actions	Updated
cmux166	Ready	Preview	Sep 8, 2026 2:21pm UTC
cmux41	Ready	Preview	Sep 8, 2026 2:21pm UTC

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Reviewing files that changed from the base of the PR and between 76802d5 and 8288d60.

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• Sources/TerminalController.swift

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[austinywang]

Full ci.yml dispatched on this branch: https://github.com/manaflow-ai/cmux/actions/runs/34220164195 (the Validate Swift warning budget step in tests-build-and-lag is the check that matters here).

[austinywang]

Full CI on this branch stops at web-typecheck (scripts/check-devbox-image-reachable.ts(148,17): error TS2339: Property 'main' does not exist on type 'ImportMeta'), a break on current main that #12154 fixes; linux-preflight then skips the macOS jobs, so the Validate Swift warning budget step has not run yet here. The change is a one-line var → let on a value returned unchanged; I will re-dispatch once #12154 lands so the budget step can confirm the count.

[austinywang]

#12154 landed; rebased onto main and re-dispatched full CI: https://github.com/manaflow-ai/cmux/actions/runs/34220955654

[austinywang]

After rebasing onto main (post #12154), full CI reached the warning-budget step: https://github.com/manaflow-ai/cmux/actions/runs/34220955654. The TerminalController.swift payload finding is gone, which is what this PR fixes. The step is still red because four newer warnings landed on main since the budget was last refreshed, none in files this PR touches:

• Sources/SessionIndexTableController.swift: call to main actor-isolated instance method reconcilePresentation(in:) in a synchronous nonisolated context
• Sources/SessionIndexTableController.swift: main actor-isolated property isApplyingRows can not be referenced from a Sendable closure
• Sources/Surfaces/CmuxTuiSnapshotParser.swift: default will never be executed
• Sources/Surfaces/SurfaceCatalogModel.swift: immutable value rowID was never used

swift-package-tests also failed once on SSHPTYAttachRetryScriptBuilderTests.signalInterruptsReconnectBackoffPromptly (a timing-based package test unrelated to this change). Those belong to their own follow-ups; this PR stays a one-line let.

[austinywang]

Heads-up: #12168 fixes the remaining four post-refresh warnings you listed (SessionIndexTableController isolation ×2, CmuxTuiSnapshotParser unreachable default, SurfaceCatalogModel unused rowID) plus the CmuxTerminal test compile break (#12161), and includes this PR's let payload line byte-identically so the two merge cleanly in either order. If #12168 lands first this PR becomes a no-op; if this lands first, #12168 rebases trivially.

[austinywang]

main now contains this exact let payload change via #12168 (3297e5e), which also cleared the other over-budget warnings; this PR can be closed as superseded.

[teamleaderleo]

Closing as already on main: merging this branch into main at 8421357 produces main's own tree, so there's nothing left to land. The branch is kept; reopen if something here is still missing. Part of the backlog cleanup in manaflow-ai/cmuxterm-hq#563.