feat: add trajectory compaction for PR merges

[khaliqgant]

Summary

Add trail compact command to consolidate multiple trajectories into a summarized form with grouped decisions. Reduces context accumulation after PR merges.

Problem

As trajectories accumulate, the context becomes noisy. Similar decisions across multiple trajectories need to be consolidated for better understanding.

Solution

CLI Command: trail compact

# Compact trajectories from the last 7 days
trail compact --since 7d

# Compact trajectories for a specific PR
trail compact --pr 123

# Compact specific trajectories
trail compact --ids traj_abc,traj_xyz

# Preview without saving
trail compact --since 7d --dry-run

Automatic GitHub Action

Workflow triggers on PR merge and runs compaction automatically:

on:
  pull_request:
    types: [closed]

jobs:
  compact:
    if: github.event.pull_request.merged
    steps:
      - run: npx trail compact --pr ${{ github.event.number }}

What Gets Compacted

• Decision grouping by category (architecture, api, database, testing, security, performance, tooling, naming, compliance)
• Key learnings aggregated across trajectories
• Files affected consolidated
• Commits linked
• Date range tracked

Output

Compacted trajectories saved to .trajectories/compacted/ with structure:

• Source trajectory IDs
• Grouped decisions with reasoning
• Summary statistics
• Key learnings

Test plan

• Build succeeds
• trail compact --help shows options
• trail compact --dry-run previews compaction
• GitHub Action workflow syntax is valid

🤖 Generated with Claude Code

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[devin-ai-integration]

Devin Review found 1 new potential issue.

View 15 additional findings in Devin Review.

[devin-ai-integration]

🔴 Overly broad --pr regex causes false-positive trajectory matching

The regex used to match trajectories by PR number is #${escaped}\b|PR.*${escaped}\b with the i (case-insensitive) flag. The PR.*${escaped}\b branch is far too permissive: PR with i matches any two-letter substring "pr" found in common English words (Improve, Express, Properly, Present, Provide, etc.), and .* allows any characters between that substring and the PR number.

Root cause and impact

For example, with --pr 5, the pattern becomes #5\b|PR.*5\b (case-insensitive). This matches a trajectory titled "Improve error handling for module 15" because:

1. "Improve" contains the substring "pr" (at positions 2–3: I-m-p-r-o-v-e), satisfying the PR part.
2. .* matches everything in between.
3. "15" ends with "5" at a word boundary, satisfying 5\b.

For single-digit PR numbers (1–9), nearly every trajectory whose title or description contains a word with "pr" and any occurrence of that digit would be falsely matched. This is especially impactful in the GitHub Actions workflow (compact-on-merge.yml:43) which falls back to --pr ${{ github.event.pull_request.number }} — for early PRs in a repository this would compact unrelated trajectories together, producing an incorrect summary.

Expected: Only trajectories explicitly referencing the PR (e.g., "PR #5", "#5") are matched.
Actual: Trajectories with incidental occurrences of "pr" (in common words) and the digit anywhere later in the text are matched.

Suggested change

	const prPattern = new RegExp(
	`#${escaped}\\b|PR.*${escaped}\\b`,
	"i",
	);
	const matchesPR =
	prPattern.test(trajectory.task.title) ||
	prPattern.test(trajectory.task.description || "") ||
	trajectory.commits.some((c) => prPattern.test(c));
	const prPattern = new RegExp(
	`#${escaped}\\b|\\bPR\\s*#?\\s*${escaped}\\b`,
	"i",
	);
	const matchesPR =
	prPattern.test(trajectory.task.title) ||
	prPattern.test(trajectory.task.description || "") ||
	trajectory.commits.some((c) => prPattern.test(c));

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