#21955: fix(line): remove redundant group:/room: prefix from buildPeerId (#21907)

## Summary - **Bug**: LINE `buildPeerId` adds redundant `group:`/`room:` prefix to peer IDs, breaking binding route matching. - **Root cause**: `buildPeerId()` in `src/line/bot-message-context.ts` prepends `group:` to `source.groupId` and `room:` to `source.roomId`, but `matchesBindingScope()` compares peer IDs as raw strings — the binding's `peer.id` never matches the prefixed runtime value. - **Fix**: Return raw `source.groupId`/`source.roomId` from `buildPeerId()` without prefix. Fixes #21907 ## Problem `buildPeerId()` returns `group:${source.groupId}` for group messages. This value is passed as `peer.id` to `resolveAgentRoute()`. The binding system does strict string comparison in `matchesBindingScope()`: ``` scope.peer.id !== match.peer.id ``` - Runtime peer.id: `group:cc7e3bece...` (with prefix) - Binding peer.id: `cc7e3bece...` (raw, as configured by user) - Result: no match → falls through to default agent **Before fix:** ``` Input: source.groupId = "Cc7e3bece1234567890abcdef" Output: peer.id = "group:Cc7e3bece1234567890abcdef" Route: agentId = "main" (default, binding not matched) Session key: agent:main:line:group:group:cc7e3bece... (double prefix) ``` ## Changes - `src/line/bot-message-context.ts` — Remove `group:`/`room:` prefix from `buildPeerId()`, return raw IDs **After fix:** ``` Input: source.groupId = "Cc7e3bece1234567890abcdef" Output: peer.id = "Cc7e3bece1234567890abcdef" Route: agentId = "line-group-agent" (binding matched) Session key: agent:line-group-agent:line:group:cc7e3bece... (correct) ``` ## Test plan - [x] New test: group peer binding matches raw groupId without prefix - [x] New test: room peer binding matches raw roomId without prefix - [x] All 4 existing `bot-message-context` tests pass - [x] Format and lint pass ## Effect on User Experience **Before:** LINE group/room messages always route to the default agent, ignoring peer-based bindings. **After:** LINE group/room messages correctly route to the agent specified in peer-based bindings. <!-- greptile_comment --> <h3>Greptile Summary</h3> This PR fixes a bug where LINE group and room messages always routed to the default agent because `buildPeerId()` was prepending `group:` and `room:` prefixes that didn't match user-configured binding peer IDs. **Key changes:** - Removed `group:` and `room:` prefixes from `buildPeerId()` return values in `src/line/bot-message-context.ts:52-57` - Added comprehensive test coverage for both group and room peer binding scenarios - Updated CHANGELOG.md with clear description of the fix **How it works:** The binding system in `matchesBindingScope()` (`src/routing/resolve-route.ts:274`) performs strict string comparison between `scope.peer.id` and `match.peer.id`. Previously, `buildPeerId()` returned prefixed values like `group:Cc7e3bece...` while user bindings contained raw IDs like `Cc7e3bece...`, causing mismatches. The fix returns raw IDs directly. **Impact verification:** - The `line:group:` and `line:room:` prefixes are still correctly added in `resolveLineAddresses()` (`src/line/bot-message-context.ts:201-203`) for message addresses - The `send.ts` normalizer already strips these prefixes when processing targets (`src/line/send.ts:43-44`) - Existing tests for group routing still pass, verifying addresses remain correct <h3>Confidence Score: 5/5</h3> - This PR is safe to merge - it's a focused bug fix with comprehensive test coverage - The fix is surgical and well-tested: removes only the problematic prefixes from `buildPeerId()` (2 lines changed), adds 2 new tests covering both group and room scenarios, and all existing tests pass. The addresses/session keys in other parts of the codebase correctly retain their `line:group:` and `line:room:` prefixes, so no side effects are expected - No files require special attention _{Last reviewed commit: b14538c} <!-- greptile_other_comments_section --> <!-- /greptile_comment -->