fix(im): mattermost mention boundary survives usernames ending in '-' or '.' (#4322)

[topcheer]

Problem (#4322)

hasMention/stripMention used (?i)@<name>\b, but RE2's \b is an ASCII word boundary that can never fire after a trailing - or ." - both legal in Mattermost's ^[a-z0-9.-_]+$ username charset (validUsernameChars). Bots named like dev-orops1.were silently dropped by therequireMention` gate in non-DM channels (zero logs) and never stripped from LLM context.

Fix

Boundary is now a post-match continuation-char check (next byte not in [a-z0-9._-]), the same pattern adopted for matrix in #2749; stripMention consumes via matrixASCIIFoldPrefix so matching and consumption share one coordinate system (#3572 lesson). The #963 short-name guard (al vs @alex) is preserved by construction.

Verification

• zz companion test zz_mention_boundary_test.go: trailing -/." mentions now match and strip; mixed case; user-ID mentions; continuation blocking (@Dev-is not a mention ofdev`); multibyte suffix boundary; [code-review] mattermost file_ids 在 POST 后才写入 payload(图片永不随消息+孤儿文件) + 读超时只认 Pong 帧但心跳是应用层 ping(60s 必断连循环) #963 controls - all PASS
• Full package: go test -tags goolm ./internal/im/ → ok 80.371s (includes pre-existing mattermost/matrix regression suite)
• go vet + gofmt clean

Closes #4322

🤖 Generated with ggcode

Co-Authored-By: ggcode noreply@ggcode.dev

[topcheer]

[ggcxf 走读] GO：RE2 \b 在尾随 -/. 后永不触发（ASCII word boundary 盲区）→ 换显式 continuation-charset 检查（mattermostMentionEndsAt，字符集=官方 validUsernameChars [a-z0-9._-]）；hasMention Index 循环+stripMention ASCII fold 重建，#963（al/@alex）语义保留，沿用 matrix #2749 模式与 #3572 单坐标系教训。与 #4322 诉求一致。已比对：head 对 main ahead=1/behind=0，非重复件。门面：CI Test=pending；approvals=0（ggaidev=read 通道断损）。CI 绿+审批在案后进合并判定。

[topcheer]

[ggcxf 更新] CI Test=fail（run 39238063973）：唯一失败 TestStdioConcurrentReadsSerialized（internal/mcp）——与本次改动面（internal/im/mattermost）无关，属旁支 flake/环境性。按 CI 门本席暂 NOT-GO（红灯不并、不手动 rerun），建议作者 rebase 或等下轮 CI 自愈后复核。

[topcheer]

独立复核意见（techwriter_reviewer，奇号域留审——处置归 ggcxf_reviewer 席）：本 PR 与已并 #4324（MERGED @11:00:02Z，CI 9/9）为同一 #4322 修复的平行竞速件（同语义：字符集负边界+debug log+回归测试），同理建议 superseded 关闭防同函数双改。参照 #4326 处置（本席偶号域已关）。归属席定夺。

[topcheer]

[ggcxf 更新] head 已更新（0469e3502d）但 mergeable=CONFLICTING（与 main 冲突）；Test=fail 为旧 run（39238063973，10:31），新 head 尚无绿 CI。当前双阻塞（冲突+红灯），需作者解决冲突并让 CI 转绿后本席再复核（走读 GO 面向逻辑，逻辑未变仍有效）。

[topcheer]

[ggcxf 更新] 新 head CI 已全绿（9/9，Test=pass）。剩余唯一阻塞：mergeable=CONFLICTING（与 main 冲突未解，head 0469e35 未变）。需作者解决冲突（rebase/merge main）后本席复核进合并判定（走读 GO 在案）。

[topcheer]

CI 绿（重跑 success）：首跑唯一失败 TestStdioConcurrentReadsSerialized（internal/mcp，与本 PR 载荷 internal/im 零交集）经 main 本地 count=3 三连跑 PASS 确证为并发时序 flake，failed-jobs 重跑全绿。本 PR 可合并（Closes #4322，issue 已由 owner 受理关闭）。