feat: /model slash command with native Discord autocomplete

[sh14y]

Design discussion: https://discord.com/channels/1491295327620169908/1491365157010542652/1493920430283686049

Summary

Adds runtime model switching via Discord's native /model slash command, with autocomplete-driven model selection.

What changed

This PR contains three commits that build on each other:

1. feat: add !model command for runtime model switching via session/set_model

   • Wires up the ACP session/set_model JSON-RPC method (verified on Kiro CLI v1.29.3)
   • Parses models.availableModels from session/new response
   • Adds alias resolution: auto, opus, sonnet, haiku
   • Initial text-based !model interface (superseded in commit 3 below)

2. fix: self-bootstrap kiro creds and config.toml inside the binary

   • Required for the cloud deployment we're using to test this; restores credentials from KIRO_CRED_B64 and generates config.toml from env vars when missing. Idempotent — no-op when files already exist.

3. feat: replace !model text command with /model slash command + autocomplete ← the main UX change

   • Removes the !model text intercept entirely
   • Registers /model as a guild command on ready() for instant propagation
   • Adds interaction_create handler for both Command and Autocomplete interactions
   • SessionPool gains a cached_models snapshot updated on every session/new, so autocomplete can answer within Discord's 3-second deadline without spawning a fresh agent (~10s cold start)
   • Background warmup task at startup populates the model cache before first use
   • Aliases (auto, opus, sonnet, haiku) appear in autocomplete as friendly shortcuts only when their target model is actually available
   • The set path defers the response since cold session creation can exceed 3s

UX

Action	Result
Type /m in Discord	Native command picker shows /model
Tab into the model field	Autocomplete returns aliases + all available model ids (current model marked)
Pick with ↑↓, hit enter	Bot defers, sets the model on the channel/thread session, replies ✅ Switched to <id>
/model with no argument	Bot replies with the full list and marks the current selection

Important: bot invite scope

/model will not appear unless the bot is invited with both bot and applications.commands OAuth scopes. Existing installations with only bot scope must re-invite using a new URL — the bot account stays the same and no data is lost.

The README has been updated to call this out in the Quick Start section.

Test plan

• cargo build --release clean
• /model (no arg) lists all available models with current marker — verified
• /model auto switches and replies ✅ Switched to auto — verified
• Verify /model sonnet resolves alias and switches
• Verify autocomplete shows live filtered suggestions as you type
• Verify allowlist (channel + user) is enforced for the slash command path

[thepagent]

Native Discord slash command with autocomplete and model caching is a nice feature but touches multiple components (Discord API registration, SessionPool, autocomplete). Could you please create a Discord discussion thread and add the link to this PR description for design tracking? Thanks! 🙏

[thepagent]

DC https://discord.com/channels/1491295327620169908/1491365157010542652/1493920430283686049

[thepagent]

Related issues worth noting alongside this PR:

• feat: /close command to manually terminate a thread session #40 feat: /close command — another Discord slash command FR; could be implemented using the same interaction handler pattern established here.
• feat: add !model command for runtime model switching via session/set_model (Kiro backend) #185 — the text-based !model predecessor; this PR supersedes it and feat: add !model command for runtime model switching via session/set_model (Kiro backend) #185 can likely be closed.

The cached_models approach for beating Discord's 3-second autocomplete deadline is a clean solution. One thing still open per the test plan: allowlist enforcement (channel + user) for the slash command path — worth tracking before merge.