Avoid rewriting escaped backslashes during JSON repair

The fallback replacement pattern also matches the second slash in already-valid escapes like \\p, so if a payload contains both one invalid escape (for example \q) and another field with a valid escaped backslash, this transform can turn the valid field into \\\p and keep the whole payload unparsable. In that mixed case we end up acknowledging with HTTP 200 and dropping an activity that was actually recoverable, which undermines the intended resilience improvement.

Useful? React with 👍 / 👎.

Regex corrupts valid \\x sequences in mixed-validity payloads

The repair regex /\\([^"\\/bfnrtu])/g scans left-to-right without tracking whether a backslash is already part of a valid \\ escape. When a payload contains a valid \\ followed by a non-escape character (e.g. \\path) alongside an invalid sequence that forces a repair pass, the regex can corrupt the valid part.

Concrete example:

• Raw JSON: {"text":"test\\path","other":"\q"}
• JSON.parse fails on \q
• The regex scans \\path:
  • Position n (\): next char is \, which IS in the exclusion set → no match at position n
  • Position n+1 (\): next char is p, which is NOT in the exclusion set → match, replaces \p with \\p
• Repaired text: {"text":"test\\\path","other":"\\q"}
• \\\path still contains \p → JSON.parse fails again → falls through to HTTP 200

In most mixed-validity cases the corruption just re-causes a parse failure (still returns 200), but for certain \\\q-style inputs (odd count of backslashes before an invalid escape character) the repaired string can parse successfully with a silently wrong value.

A conservative improvement is to use a lookbehind to skip escaped backslashes:

Note: a negative lookbehind (?<!\\) skips a \ that is itself already escaped, preventing the regex from "reaching into" a valid \\ pair. For complete correctness a character-by-character state machine is ideal, but the lookbehind substantially improves the common cases.

This is a comment left during a code review.
Path: extensions/msteams/src/monitor.ts
Line: 289

Comment:
**Regex corrupts valid `\\x` sequences in mixed-validity payloads**

The repair regex `/\\([^"\\/bfnrtu])/g` scans left-to-right without tracking whether a backslash is already part of a valid `\\` escape. When a payload contains a valid `\\` followed by a non-escape character (e.g. `\\path`) *alongside* an invalid sequence that forces a repair pass, the regex can corrupt the valid part.

**Concrete example:**
- Raw JSON: `{"text":"test\\path","other":"\q"}`
- `JSON.parse` fails on `\q`
- The regex scans `\\path`:
  - Position n (`\`): next char is `\`, which IS in the exclusion set → no match at position n
  - Position n+1 (`\`): next char is `p`, which is NOT in the exclusion set → **match, replaces `\p` with `\\p`**
- Repaired text: `{"text":"test\\\path","other":"\\q"}`
- `\\\path` still contains `\p` → `JSON.parse` fails again → falls through to HTTP 200

In *most* mixed-validity cases the corruption just re-causes a parse failure (still returns 200), but for certain `\\\q`-style inputs (odd count of backslashes before an invalid escape character) the repaired string can parse successfully with a silently wrong value.

A conservative improvement is to use a lookbehind to skip escaped backslashes:

```suggestion
        const fixed = rawText.replace(/(?<!\\)\\([^"\\/bfnrtu])/g, "\\\\$1");
```

Note: a negative lookbehind `(?<!\\)` skips a `\` that is itself already escaped, preventing the regex from "reaching into" a valid `\\` pair. For complete correctness a character-by-character state machine is ideal, but the lookbehind substantially improves the common cases.

How can I resolve this? If you propose a fix, please make it concise.

express.raw(...) is newly used here, but the MS Teams monitor lifecycle test mocks the express module without providing a raw export. This will cause the test suite to throw at startup when express.raw is undefined. Update the mock in extensions/msteams/src/monitor.lifecycle.test.ts to include a raw() middleware factory (similar to how json() is mocked) so tests continue to run.

The repair regex can accidentally corrupt already-valid escaped backslashes when the payload contains both valid sequences like \\p and a separate invalid escape that triggers the repair path. Example: if parsing fails elsewhere, \\p (valid) can become \\\p (invalid), preventing recovery. Consider only rewriting backslashes that are not themselves escaped (e.g. using a negative lookbehind like (?<!\\)\\([^"\\/bfnrtu])).

This change introduces several new behaviors (raw body parsing, escape-sequence repair, and returning HTTP 200 on unrecoverable JSON) but there are no unit tests covering them. Since this module already has lifecycle/timeouts tests, please add coverage for: (1) a payload with an invalid escape like \p being repaired and passed to the adapter, and (2) an unrecoverable JSON parse returning 200 (and not invoking the adapter) to prevent Azure backoff.

Restrict escape repair to truly bare backslashes

The repair regex also matches the second slash of already-valid escaped backslashes (for example \\p), so when a payload contains one invalid escape (\q) plus another field with a valid escaped backslash, rawText.replace(/\\([^"\\/bfnrtu])/g, "\\\\$1") rewrites the valid field into an invalid sequence and the second parse still fails. In that mixed-input case the handler returns HTTP 200 and drops an activity that should have been recoverable, which defeats the resilience improvement for real Teams payloads containing both kinds of strings.

Useful? React with 👍 / 👎.

Restrict first regex branch to escaped backslashes only

The new repair regex uses (\\.)+ as its first alternation branch, which matches any backslash escape (including invalid ones like \q), so the replacement callback returns those matches unchanged instead of repairing them. In practice, payloads containing bare escapes (for example "Test\Project") remain invalid after repairJsonEscapes, the second JSON.parse still fails, and the middleware drops otherwise recoverable activities via the SyntaxError 200-ack path, which defeats the stated resilience fix.

Useful? React with 👍 / 👎.