🤖 Generated by AI (CnsMaple + Reasonix)

Summary

Replace the strict strings.HasPrefix filter in the chat-TUI slash-command
completion popup with a case-insensitive subsequence matcher, so typing a
partial token like /mdl surfaces /compact, /model, /memory and any
other command whose letters appear in order — not just commands that begin
with the typed prefix.

Why

Users naturally abbreviate or fat-finger slash commands (/compt,
/mdl, /skll, /brnch). The current matcher silently closes the menu on
anything that isn't an exact prefix, forcing the user to retype or look
the command up via /help. A subsequence match keeps the "type a few
letters, see the candidates" muscle memory from shells like fzf.

Scope

Inentionally limited to the live TUI completion popup. Typed-input
resolution (/name + Enter) and the model's slash_command tool still
use exact-name lookup, so the routing layer stays predictable. Both are
one-liner follow-ups if reviewers want them in the same change.

Implementation

• internal/cli/complete.go
  • New fuzzyFilterSlash(items, query): returns the matched compItems
    with prefix hits ranked first, subsequence-only hits after, each
    group preserving the original slashItems() order. Empty query
    lists everything (same as before). Zero matches returns nil so
    updateCompletion falls through and closes the menu.
  • New subsequenceMatch(target, query): rune-level subsequence test
    on already-case-folded strings. O(n+m), no allocations beyond the
    rune slice.
  • updateCompletion slash branch: filterByPrefix(...) →
    fuzzyFilterSlash(...). No other call sites touched.

Tests

8 new tests in internal/cli/complete_test.go:

• TestFuzzyFilterSlashSubsequence — /mdl hits /model, not /mcp
• TestFuzzyFilterSlashPrefixFirst — /mo ranks /model first
• TestFuzzyFilterSlashCaseInsensitive — /COMP hits /compact
• TestFuzzyFilterSlashEmptyQueryMatchesAll — bare / lists everything
• TestFuzzyFilterSlashNoMatchClosesMenu — /xzqzqz closes the menu
• TestFuzzyFilterSlashAppliesToCustomCommands — custom commands covered
• TestFuzzyFilterSlashAcceptFillsInput — Tab/accept end-to-end
• TestSubsequenceMatchUnit — direct matcher coverage incl. negatives

All 4 pre-existing slash-completion tests still pass. gofmt -l and
go vet ./internal/cli/... are clean. The 4 unrelated failures in
internal/cli/... (TestApplyMCPModeDropsLegacyTier,
TestModelRefsSkipsUnconfigured, TestOneLine, TestRenderRewindSmoke)
are pre-existing on main-v2 and were verified with git stash to be
unrelated to this change.

Risk

Low. The matcher is a strict superset of the previous prefix filter:
every input that matched before still matches, and the menu's
"open/close" contract is preserved (empty = list all, no match = close).
The accept/insert path is untouched, so Tab still fills the input with
the top-ranked hit's insert string.

Checklist

• Rebased onto current upstream/main-v2 (was 51 commits behind)
• gofmt -l internal/cli/... clean on the LF content git will push
• go vet ./internal/cli/... clean
• New + existing slash-completion tests pass
• PR targets main-v2 per CONTRIBUTING.md