Emit accepted line fingerprint analytics (#21601)

## Why

Codex assisted-code attribution needs a client-side accepted-code source
that does not upload raw code. This adds a hash-only analytics event
derived from the turn diff so downstream attribution can compare
accepted Codex lines against commit or PR diffs.

## What Changed

- Parse accepted/effective added lines from the final turn diff and emit
`codex_accepted_line_fingerprints` analytics.
- Hash repo, path, and normalized line content before upload; raw code
and raw diffs are not included in the event.
- Chunk large fingerprint payloads and send accepted-line fingerprint
events in isolated requests while preserving normal batching for other
analytics events.
- Canonicalize Git remote URLs before repo hashing so SSH/HTTPS GitHub
remotes join to the same repo hash.
- Add parser coverage for unified diff hunk lines that look like `+++`
or `---` file headers.

## Verification

- `cargo test -p codex-analytics`
- `cargo test -p codex-git-utils canonicalize_git_remote_url`
- `just fix -p codex-analytics`
- `just bazel-lock-check`
- `git diff --check`

codex-rs/analytics/src/accepted_lines.rs

@@ -0,0 +1,298 @@
+use crate::events::CodexAcceptedLineFingerprintsEventParams;
+use crate::events::CodexAcceptedLineFingerprintsEventRequest;
+use crate::events::TrackEventRequest;
+use crate::facts::AcceptedLineFingerprint;
+use codex_git_utils::canonicalize_git_remote_url;
+use codex_git_utils::get_git_remote_urls_assume_git_repo;
+use sha1::Digest;
+use std::path::Path;
+
+const ACCEPTED_LINE_FINGERPRINT_EVENT_TARGET_BYTES: usize = 2 * 1024 * 1024;
+const ACCEPTED_LINE_FINGERPRINT_EVENT_FIXED_BYTES: usize = 1024;
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct AcceptedLineFingerprintSummary {
+    pub accepted_added_lines: u64,
+    pub accepted_deleted_lines: u64,
+    pub line_fingerprints: Vec<AcceptedLineFingerprint>,
+}
+
+pub(crate) struct AcceptedLineFingerprintEventInput {
+    pub(crate) event_type: &'static str,
+    pub(crate) turn_id: String,
+    pub(crate) thread_id: String,
+    pub(crate) product_surface: Option<String>,
+    pub(crate) model_slug: Option<String>,
+    pub(crate) completed_at: u64,
+    pub(crate) repo_hash: Option<String>,
+    pub(crate) accepted_added_lines: u64,
+    pub(crate) accepted_deleted_lines: u64,
+    pub(crate) line_fingerprints: Vec<AcceptedLineFingerprint>,
+}
+
+pub fn accepted_line_fingerprints_from_unified_diff(
+    unified_diff: &str,
+) -> AcceptedLineFingerprintSummary {
+    let mut current_path: Option<String> = None;
+    let mut in_hunk = false;
+    let mut accepted_added_lines = 0;
+    let mut accepted_deleted_lines = 0;
+    let mut line_fingerprints = Vec::new();
+
+    for line in unified_diff.lines() {
+        if line.starts_with("diff --git ") {
+            current_path = None;
+            in_hunk = false;
+            continue;
+        }
+
+        if line.starts_with("@@ ") {
+            in_hunk = true;
+            continue;
+        }
+
+        if !in_hunk && let Some(path) = line.strip_prefix("+++ ") {
+            current_path = normalize_diff_path(path);
+            continue;
+        }
+
+        if !in_hunk && line.starts_with("--- ") {
+            continue;
+        }
+
+        if let Some(added_line) = line.strip_prefix('+') {
+            accepted_added_lines += 1;
+            if let Some(path) = current_path.as_deref()
+                && let Some(normalized_line) = normalize_effective_line(added_line)
+            {
+                line_fingerprints.push(AcceptedLineFingerprint {
+                    path_hash: fingerprint_hash("path", path),
+                    line_hash: fingerprint_hash("line", &normalized_line),
+                });
+            }
+            continue;
+        }
+
+        if line.starts_with('-') {
+            accepted_deleted_lines += 1;
+        }
+    }
+
+    AcceptedLineFingerprintSummary {
+        accepted_added_lines,
+        accepted_deleted_lines,
+        line_fingerprints,
+    }
+}
+
+pub fn fingerprint_hash(domain: &str, value: &str) -> String {
+    let mut hasher = sha1::Sha1::new();
+    hasher.update(b"file-line-v1\0");
+    hasher.update(domain.as_bytes());
+    hasher.update(b"\0");
+    hasher.update(value.as_bytes());
+    format!("{:x}", hasher.finalize())
+}
+
+pub(crate) fn accepted_line_fingerprint_event_requests(
+    input: AcceptedLineFingerprintEventInput,
+) -> Vec<TrackEventRequest> {
+    let chunks = accepted_line_fingerprint_chunks(input.line_fingerprints);
+    chunks
+        .into_iter()
+        .enumerate()
+        .map(|(index, line_fingerprints)| {
+            let is_first_chunk = index == 0;
+            TrackEventRequest::AcceptedLineFingerprints(Box::new(
+                CodexAcceptedLineFingerprintsEventRequest {
+                    event_type: "codex_accepted_line_fingerprints",
+                    event_params: CodexAcceptedLineFingerprintsEventParams {
+                        event_type: input.event_type,
+                        turn_id: input.turn_id.clone(),
+                        thread_id: input.thread_id.clone(),
+                        product_surface: input.product_surface.clone(),
+                        model_slug: input.model_slug.clone(),
+                        completed_at: input.completed_at,
+                        repo_hash: input.repo_hash.clone(),
+                        accepted_added_lines: if is_first_chunk {
+                            input.accepted_added_lines
+                        } else {
+                            0
+                        },
+                        accepted_deleted_lines: if is_first_chunk {
+                            input.accepted_deleted_lines
+                        } else {
+                            0
+                        },
+                        line_fingerprints,
+                    },
+                },
+            ))
+        })
+        .collect()
+}
+
+pub async fn accepted_line_repo_hash_for_cwd(cwd: &Path) -> Option<String> {
+    let remotes = get_git_remote_urls_assume_git_repo(cwd).await?;
+    remotes
+        .get("origin")
+        .or_else(|| remotes.values().next())
+        .map(|remote_url| {
+            let canonical_remote_url =
+                canonicalize_git_remote_url(remote_url).unwrap_or_else(|| remote_url.to_string());
+            fingerprint_hash("repo", &canonical_remote_url)
+        })
+}
+
+fn normalize_diff_path(path: &str) -> Option<String> {
+    let path = path.trim();
+    if path == "/dev/null" {
+        return None;
+    }
+
+    Some(
+        path.strip_prefix("b/")
+            .or_else(|| path.strip_prefix("a/"))
+            .unwrap_or(path)
+            .to_string(),
+    )
+}
+
+fn normalize_effective_line(line: &str) -> Option<String> {
+    let normalized = line.split_whitespace().collect::<Vec<_>>().join(" ");
+    if normalized.len() <= 3 {
+        return None;
+    }
+    if !normalized
+        .chars()
+        .any(|ch| ch.is_alphanumeric() || ch == '_')
+    {
+        return None;
+    }
+    Some(normalized)
+}
+
+fn accepted_line_fingerprint_chunks(
+    line_fingerprints: Vec<AcceptedLineFingerprint>,
+) -> Vec<Vec<AcceptedLineFingerprint>> {
+    if line_fingerprints.is_empty() {
+        return vec![Vec::new()];
+    }
+
+    let mut chunks = Vec::new();
+    let mut current = Vec::new();
+    let mut current_bytes = ACCEPTED_LINE_FINGERPRINT_EVENT_FIXED_BYTES;
+
+    for fingerprint in line_fingerprints {
+        let item_bytes = accepted_line_fingerprint_json_bytes(&fingerprint);
+        let separator_bytes = usize::from(!current.is_empty());
+        if !current.is_empty()
+            && current_bytes + separator_bytes + item_bytes
+                > ACCEPTED_LINE_FINGERPRINT_EVENT_TARGET_BYTES
+        {
+            chunks.push(current);
+            current = Vec::new();
+            current_bytes = ACCEPTED_LINE_FINGERPRINT_EVENT_FIXED_BYTES;
+        }
+        current_bytes += usize::from(!current.is_empty()) + item_bytes;
+        current.push(fingerprint);
+    }
+
+    if !current.is_empty() {
+        chunks.push(current);
+    }
+    chunks
+}
+
+fn accepted_line_fingerprint_json_bytes(fingerprint: &AcceptedLineFingerprint) -> usize {
+    // {"path_hash":"...","line_hash":"..."} plus one byte of array comma
+    // accounted for by the caller when needed.
+    32 + fingerprint.path_hash.len() + fingerprint.line_hash.len()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn parses_counts_and_effective_added_fingerprints() {
+        let diff = "\
+diff --git a/src/lib.rs b/src/lib.rs
+index 1111111..2222222
+--- a/src/lib.rs
++++ b/src/lib.rs
+@@ -1,3 +1,5 @@
+-old line
++fn useful() {
++}
++    return user.id;
+ context
+";
+
+        let summary = accepted_line_fingerprints_from_unified_diff(diff);
+
+        assert_eq!(
+            summary,
+            AcceptedLineFingerprintSummary {
+                accepted_added_lines: 3,
+                accepted_deleted_lines: 1,
+                line_fingerprints: vec![
+                    AcceptedLineFingerprint {
+                        path_hash: fingerprint_hash("path", "src/lib.rs"),
+                        line_hash: fingerprint_hash("line", "fn useful() {"),
+                    },
+                    AcceptedLineFingerprint {
+                        path_hash: fingerprint_hash("path", "src/lib.rs"),
+                        line_hash: fingerprint_hash("line", "return user.id;"),
+                    },
+                ],
+            }
+        );
+    }
+
+    #[test]
+    fn skips_added_file_metadata_headers() {
+        let diff = "\
+diff --git a/new.py b/new.py
+new file mode 100644
+index 0000000..1111111
+--- /dev/null
++++ b/new.py
+@@ -0,0 +1 @@
++print('hello')
+";
+
+        let summary = accepted_line_fingerprints_from_unified_diff(diff);
+
+        assert_eq!(summary.accepted_added_lines, 1);
+        assert_eq!(summary.accepted_deleted_lines, 0);
+        assert_eq!(summary.line_fingerprints.len(), 1);
+    }
+
+    #[test]
+    fn parses_hunk_lines_that_look_like_file_headers() {
+        let diff = "\
+diff --git a/src/lib.rs b/src/lib.rs
+index 1111111..2222222
+--- a/src/lib.rs
++++ b/src/lib.rs
+@@ -1,2 +1,2 @@
+--- old value
++++ new value
+";
+
+        let summary = accepted_line_fingerprints_from_unified_diff(diff);
+
+        assert_eq!(
+            summary,
+            AcceptedLineFingerprintSummary {
+                accepted_added_lines: 1,
+                accepted_deleted_lines: 1,
+                line_fingerprints: vec![AcceptedLineFingerprint {
+                    path_hash: fingerprint_hash("path", "src/lib.rs"),
+                    line_hash: fingerprint_hash("line", "++ new value"),
+                }],
+            }
+        );
+    }
+}