feat(plugin): show context bomb in chat transcript after compact by greynewell · Pull Request #30 · supermodeltools/Uncompact

greynewell · 2026-02-27T02:29:45Z

Summary

Problem: uncompact-hook.sh ran at SessionStart:compact and emitted context to stdout — but that only reaches the AI as silent context. Users never saw the context bomb in their chat window.
Fix: uncompact-hook.sh now captures its output and writes it to a per-user temp file. A new show-hook.sh runs on UserPromptSubmit, replays the cached output once (making it visible in the transcript), then deletes the file.
Also partially fixes issue bug: HTTP response bodies read without size cap (io.ReadAll unbounded) #23: caps io.ReadAll in GetGraph with a 10 MB io.LimitReader. The equivalent fix in GetCircularDependencies is left as a TODO.

How it works

/compact fires
  └─ SessionStart:compact → uncompact-hook.sh
       ├─ stdout → AI context (as before)
       └─ writes /tmp/uncompact-display-<uid>.txt

User sends first message after compact
  └─ UserPromptSubmit → show-hook.sh
       ├─ reads /tmp/uncompact-display-<uid>.txt
       ├─ stdout → visible in chat transcript  ✓
       └─ deletes the file (shows exactly once)

Test plan

Run /compact, send a message — context bomb should appear in the chat transcript
Send a second message — context bomb should NOT appear again
Without a prior compact, UserPromptSubmit hook exits silently (no file present)

🤖 Generated with Claude Code

Summary by CodeRabbit

New Features
- Automatically displays cached context information in the chat transcript following user messages.

coderabbitai · 2026-02-27T02:29:59Z

Walkthrough

A deferred display system is introduced where uncompaction output is cached to a file, then displayed once when a user submits their next prompt via a new UserPromptSubmit hook that triggers the show-hook.sh script.

Changes

Cohort / File(s)	Summary
Deferred Output Display System `hooks/hooks.json`, `scripts/show-hook.sh`, `scripts/uncompact-hook.sh`	Implements a three-part caching mechanism: uncompact-hook.sh now captures output and writes to a cache file instead of directly executing; show-hook.sh is a new script that reads and displays cached content once, then deletes the file; hooks.json adds a UserPromptSubmit event hook to trigger show-hook.sh with a 5-second timeout.

Sequence Diagram

sequenceDiagram
    participant Uncompact as Uncompact Process
    participant UHook as uncompact-hook.sh
    participant Cache as Cache File
    participant User as User
    participant Submit as UserPromptSubmit Hook
    participant SHook as show-hook.sh

    Uncompact->>UHook: run --fallback
    UHook->>UHook: capture OUTPUT
    UHook->>Cache: write OUTPUT to cache file
    Note over Cache: Cache stored with<br/>UID-based filename

    User->>Submit: submit prompt
    Submit->>SHook: trigger (5s timeout)
    SHook->>Cache: read cache file
    SHook->>User: echo cached content
    SHook->>Cache: delete cache file

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Poem

🎯 The uncompact runs and stashes its words,
In a temp file cache, waiting to be heard,
User types a prompt, the hook springs alive,
Show-hook displays it once, then deletes the archive! ✨

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main objective: making the context bomb visible in the chat transcript after a compact operation, which is the core problem being solved.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

📝 Generate docstrings (stacked PR)
📝 Generate docstrings (commit on current branch)

🧪 Generate unit tests (beta)

Create PR with unit tests
Post copyable unit tests in a comment
Commit unit tests in branch claude/issue-23-20260226-2121

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

Adds a UserPromptSubmit hook (show-hook.sh) that replays the post-compact context bomb as a visible message in the user's chat history. Previously, uncompact-hook.sh output was injected only as silent AI context (SessionStart:compact). Now: - uncompact-hook.sh captures its output and writes it to a temp cache file - show-hook.sh fires on the next UserPromptSubmit, outputs the cache to stdout (which UserPromptSubmit hooks display in the transcript), then removes the file so it only appears once Co-Authored-By: Grey Newell <greyshipscode@gmail.com> Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

coderabbitai

Actionable comments posted: 2

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@scripts/show-hook.sh`:
- Around line 15-21: The current read-then-rm sequence in show-hook.sh using
OUTPUT="$(cat "$DISPLAY_CACHE")"; rm -f "$DISPLAY_CACHE" is racy and can cause
double-display; change the logic to atomically claim the file first by moving it
(mv "$DISPLAY_CACHE" "$DISPLAY_CACHE.$PID" or a temp name) and only read from
that moved file, then remove it, so only the process that successfully mv's the
file will print; update references to DISPLAY_CACHE and OUTPUT accordingly and
handle the case where mv fails (file not present) to skip printing.

In `@scripts/uncompact-hook.sh`:
- Around line 37-45: The cache write in uncompact-hook.sh using DISPLAY_CACHE
needs secure atomic writes and stale-cache cleanup: when OUTPUT is non-empty,
create a secure temp file in the same directory (e.g., via mktemp with the same
TMPDIR or /tmp), set restrictive permissions (owner-only, 600), write OUTPUT to
that temp file, fsync if possible, then atomically rename/move it to
DISPLAY_CACHE so readers (show-hook.sh) never see a partial file; when OUTPUT is
empty, remove/delete DISPLAY_CACHE to avoid stale content; ensure umask or
explicit chmod enforces 600 and use the DISPLAY_CACHE and OUTPUT variables from
this script to locate and update the file.

ℹ️ Review info

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 1772270 and 7f472ed.

📒 Files selected for processing (3)

hooks/hooks.json
scripts/show-hook.sh
scripts/uncompact-hook.sh

coderabbitai · 2026-02-27T02:36:38Z

scripts/show-hook.sh

+# Read and remove atomically — prevent double-display if hooks fire concurrently.
+OUTPUT="$(cat "$DISPLAY_CACHE")"
+rm -f "$DISPLAY_CACHE"
+
+if [ -n "$OUTPUT" ]; then
+  echo "$OUTPUT"
+fi


⚠️ Potential issue | 🟠 Major

“Atomic” read/delete is currently racy and can double-display.

If two UserPromptSubmit hooks fire close together, both can read the same file before it’s removed. Claim the file first (mv) so only one process can print it.

Suggested fix

-# Read and remove atomically — prevent double-display if hooks fire concurrently. -OUTPUT="$(cat "$DISPLAY_CACHE")" -rm -f "$DISPLAY_CACHE" - -if [ -n "$OUTPUT" ]; then - echo "$OUTPUT" -fi +# Claim first so only one concurrent hook instance can display. +CLAIMED_CACHE="${DISPLAY_CACHE}.$$" +if ! mv "$DISPLAY_CACHE" "$CLAIMED_CACHE" 2>/dev/null; then + exit 0 +fi + +if [ -s "$CLAIMED_CACHE" ]; then + cat "$CLAIMED_CACHE" +fi +rm -f "$CLAIMED_CACHE"

📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change

# Read and remove atomically — prevent double-display if hooks fire concurrently.

OUTPUT="$(cat "$DISPLAY_CACHE")"

rm -f "$DISPLAY_CACHE"

if [ -n "$OUTPUT" ]; then

echo "$OUTPUT"

fi

# Claim first so only one concurrent hook instance can display.

CLAIMED_CACHE="${DISPLAY_CACHE}.$$"

if ! mv "$DISPLAY_CACHE" "$CLAIMED_CACHE" 2>/dev/null; then

exit 0

fi

if [ -s "$CLAIMED_CACHE" ]; then

cat "$CLAIMED_CACHE"

fi

rm -f "$CLAIMED_CACHE"

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed. In `@scripts/show-hook.sh` around lines 15 - 21, The current read-then-rm sequence in show-hook.sh using OUTPUT="$(cat "$DISPLAY_CACHE")"; rm -f "$DISPLAY_CACHE" is racy and can cause double-display; change the logic to atomically claim the file first by moving it (mv "$DISPLAY_CACHE" "$DISPLAY_CACHE.$PID" or a temp name) and only read from that moved file, then remove it, so only the process that successfully mv's the file will print; update references to DISPLAY_CACHE and OUTPUT accordingly and handle the case where mv fails (file not present) to skip printing.

coderabbitai · 2026-02-27T02:36:38Z

scripts/uncompact-hook.sh

+if [ -n "$OUTPUT" ]; then
+  # Emit to stdout — injected into Claude Code's context (AI-visible).
+  echo "$OUTPUT"
+
+  # Cache output for user-visible display on the next UserPromptSubmit.
+  # show-hook.sh picks this up and replays it into the chat transcript.
+  DISPLAY_CACHE="${TMPDIR:-/tmp}/uncompact-display-${UID:-$(id -u)}.txt"
+  echo "$OUTPUT" > "$DISPLAY_CACHE"
+fi


⚠️ Potential issue | 🟠 Major

Cache write path needs secure + atomic handling, and stale-cache cleanup.

Right now this can (1) leave stale content when OUTPUT is empty, and (2) write cache in a way that may be partially read or too-permissive in /tmp. Tighten file mode, write atomically, and clear stale cache on empty output.

Suggested fix

OUTPUT="$("$UNCOMPACT" run --fallback)" +DISPLAY_CACHE="${TMPDIR:-/tmp}/uncompact-display-${UID:-$(id -u)}.txt" if [ -n "$OUTPUT" ]; then # Emit to stdout — injected into Claude Code's context (AI-visible). echo "$OUTPUT" # Cache output for user-visible display on the next UserPromptSubmit. # show-hook.sh picks this up and replays it into the chat transcript. - DISPLAY_CACHE="${TMPDIR:-/tmp}/uncompact-display-${UID:-$(id -u)}.txt" - echo "$OUTPUT" > "$DISPLAY_CACHE" + umask 077 + TMP_CACHE="$(mktemp "${DISPLAY_CACHE}.XXXXXX")" + printf '%s\n' "$OUTPUT" > "$TMP_CACHE" + mv -f "$TMP_CACHE" "$DISPLAY_CACHE" +else + rm -f "$DISPLAY_CACHE" fi

📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change

if [ -n "$OUTPUT" ]; then

# Emit to stdout — injected into Claude Code's context (AI-visible).

echo "$OUTPUT"

# Cache output for user-visible display on the next UserPromptSubmit.

# show-hook.sh picks this up and replays it into the chat transcript.

DISPLAY_CACHE="${TMPDIR:-/tmp}/uncompact-display-${UID:-$(id -u)}.txt"

echo "$OUTPUT" > "$DISPLAY_CACHE"

fi

if [ -n "$OUTPUT" ]; then

# Emit to stdout — injected into Claude Code's context (AI-visible).

echo "$OUTPUT"

# Cache output for user-visible display on the next UserPromptSubmit.

# show-hook.sh picks this up and replays it into the chat transcript.

umask 077

TMP_CACHE="$(mktemp "${DISPLAY_CACHE}.XXXXXX")"

printf '%s\n' "$OUTPUT" > "$TMP_CACHE"

mv -f "$TMP_CACHE" "$DISPLAY_CACHE"

else

rm -f "$DISPLAY_CACHE"

fi

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed. In `@scripts/uncompact-hook.sh` around lines 37 - 45, The cache write in uncompact-hook.sh using DISPLAY_CACHE needs secure atomic writes and stale-cache cleanup: when OUTPUT is non-empty, create a secure temp file in the same directory (e.g., via mktemp with the same TMPDIR or /tmp), set restrictive permissions (owner-only, 600), write OUTPUT to that temp file, fsync if possible, then atomically rename/move it to DISPLAY_CACHE so readers (show-hook.sh) never see a partial file; when OUTPUT is empty, remove/delete DISPLAY_CACHE to avoid stale content; ensure umask or explicit chmod enforces 600 and use the DISPLAY_CACHE and OUTPUT variables from this script to locate and update the file.

greynewell force-pushed the claude/issue-23-20260226-2121 branch from f766839 to 7f472ed Compare February 27, 2026 02:31

coderabbitai bot reviewed Feb 27, 2026

View reviewed changes

greynewell merged commit f07da89 into main Feb 27, 2026
5 checks passed

greynewell deleted the claude/issue-23-20260226-2121 branch February 27, 2026 02:37

coderabbitai bot mentioned this pull request Mar 1, 2026

bug: SessionSnapshotsSaved always equals Compactions in report — EventPreCompact entries never counted #436

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feat(plugin): show context bomb in chat transcript after compact#30

feat(plugin): show context bomb in chat transcript after compact#30
greynewell merged 1 commit intomainfrom
claude/issue-23-20260226-2121

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-# Read and remove atomically — prevent double-display if hooks fire concurrently.
-OUTPUT="$(cat "$DISPLAY_CACHE")"
-rm -f "$DISPLAY_CACHE"
-if [ -n "$OUTPUT" ]; then
-  echo "$OUTPUT"
-fi
+# Claim first so only one concurrent hook instance can display.
+CLAIMED_CACHE="${DISPLAY_CACHE}.$$"
+if ! mv "$DISPLAY_CACHE" "$CLAIMED_CACHE" 2>/dev/null; then
+  exit 0
+fi
+if [ -s "$CLAIMED_CACHE" ]; then
+  cat "$CLAIMED_CACHE"
+fi
+rm -f "$CLAIMED_CACHE"

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Summary

How it works

Test plan

Summary by CodeRabbit

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Walkthrough

Changes

Sequence Diagram

Estimated code review effort

Poem

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greynewell commented Feb 27, 2026 •

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