comments: add parent_comment_id (threaded replies, back-filled from source DBs); document semantics

BUILD_LOG.md

@@ -94,3 +94,10 @@ release. Nothing in the accompanying paper used `step`.
 
 `tool_call` < 100% because unaligned agents carry no decision record. gpt-oss and GLM-4
 never emit visible deliberation.
+
+
+## Addendum 2026-09-28 — `comments.parquet` gains `parent_comment_id`
+
+The simulator records threaded replies (`comment.parent_comment_id`) and the first release
+dropped the column. Back-filled from the source databases; no other column, row count, or
+order changed.

README.md

@@ -73,14 +73,16 @@ All seven files share `run_id` as the primary key. `step` is the simulation tick
 | `runs.parquet` | one simulation | `run_id`, `experiment_type`, `n_agents`, `steps`, `created_at`, `step_coverage` |
 | `agents.parquet` | one agent in one run | `run_id`, `agent_id`, `model`, `persona`, `join_step` |
 | `posts.parquet` | one authored post | `run_id`, `post_id`, `agent_id`, `model`, `step`, `content` |
-| `comments.parquet` | one authored comment | `run_id`, `comment_id`, `post_id`, `agent_id`, `model`, `step`, `content`, `is_cross_model` |
+| `comments.parquet` | one authored comment | `run_id`, `comment_id`, `post_id`, `agent_id`, `model`, `step`, `content`, `is_cross_model`, `parent_comment_id` |
 | `impressions.parquet` | one post shown to one agent | `run_id`, `step`, `viewer_agent_id`, `post_id`, `slot` |
 | `actions.parquet` | one logged action | `run_id`, `agent_id`, `step`, `action`, `created_at` |
 | `trajectories.parquet` | one agent activation, active **or passive** | `run_id`, `agent_id`, `activation_idx`, `step`, `refreshed_at`, `action`, `post_id`, `tool_args`, `response_text`, `reasoning` |
 
 `model` is denormalised onto `posts` and `comments` so the common analyses need no join.
 `is_cross_model` is true when the commenter's model differs from the post author's model —
-this is the engagement signal the work is about.
+this is the engagement signal the work is about. `parent_comment_id` is set when a comment was
+filed as a threaded reply to another comment on the same post; agents do this for ~4–6% of
+comments — most replies to earlier commenters are top-level comments that address them by name.
 
 ## Two things to understand before using this
 

comments.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:e3b527acc88d0747be12821397069c82f13994dc51cea8cb704d23b2ea132b9f
-size 91803414
+oid sha256:4002b8755eea25ef4c6f1e13379164dd3d302c1de4a136afcd18fb8a9586bb69
+size 92034912