fix: remove empty tagged messages after tool drop (Issue #97)

[Zireael]

Problem (#97)

Magic Context tags visible message parts with §N§ prefixes so the agent can reference them (ctx_reduce(§3§)). Two related failure modes were reported:

1. Empty tagged messages after tool drop

When execute passes drop most tool structure, user messages that contain only a tag prefix (e.g. §424§) were not removed. hasMeaningfulPart treated the raw § characters as content. These ghost messages pollute the transcript and confuse the model.

2. Multiplying / bleeding tag numbers in chat UI

Assistant and user-visible text accumulated leading numbers and cargo-cult tag notation, e.g.:

• 2030 2030 2030° Run clippy again:
• 99 Actually executing now. Running fmt:
• Blank user messages that are only a number
• Mid-text §40827§ cargo-cult from models mimicking MC notation

Root cause (persistence vs transform mismatch):

1. The transform layer injects §N§ on each pass via prependTag / stripTagPrefix.
2. OpenCode experimental.text.complete (and Pi message_end persistence) previously stripped all § characters globally. Well-formed §2030§ became bare 2030 — digit residue with no section signs.
3. Transform stripTagPrefix only removed leading §-shaped prefixes, not bare digits. Each transform pass prepended a fresh §N§ in front of the residue → numbers stacked in persisted/UI text.
4. A blind leading-digit regex was considered but rejected: it breaks legitimate content (99 files…, 6 8 9 tasks…, 2024 roadmap, numbered lists).

Issue #97’s original fix targeted tagger/DB counter drift and empty tagged messages; it did not fully address the persistence/transform split above.

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What this PR changes

Tool drop — remove empty tagged messages

• hasMeaningfulPart in tool-drop-target.ts now uses shared stripTagPrefix before checking whether text is non-empty (well-formed and malformed leading §N§ shapes).
• Tests in tool-drop-target.test.ts cover tag-only and malformed-prefix cases.

Persistence boundary — pair-aware strip (OpenCode + Pi)

• New stripPersistedAssistantText() in tag-content-primitives.ts:
  1. Leading ^(§N§\s*)+ runs
  2. Global removal of whole §N§ pairs (not § alone)
  3. Global malformed §N">… hybrids (compartment/XML confusion)
  4. Stray lone § after pair removal
• Wired into text-complete.ts and pi-plugin/strip-tag-prefix.ts so assistant text is clean before jsonl persistence and Pi UI render.

Transform boundary — § notation only

• stripTagPrefix / prependTag strip only leading §-shaped MC notation (well-formed + malformed). They do not strip bare leading digits.
• Prevents false positives on real user/assistant content while still deduplicating tag prefixes before re-injection.

Temporal awareness

• OpenCode temporal-awareness.ts and Pi temporal-awareness-pi.ts use shared peelLeadingMcTagNotation() so gap markers insert after malformed prefixes too, not only §N§ regex matches.

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Out of scope (follow-up)

• Session-aware legacy heal for already-persisted bare-digit pollution without § (e.g. 2030 2030 2030° with no section signs). New assistant completions with well-formed §N§ pairs are cleaned at persistence; old residue may remain until rewritten.

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Test plan

• bun test packages/plugin/src/hooks/magic-context/tag-content-primitives.test.ts
• bun test packages/plugin/src/hooks/magic-context/text-complete.test.ts
• bun test packages/plugin/src/hooks/magic-context/tool-drop-target.test.ts
• bun test packages/pi-plugin/src/strip-tag-prefix.test.ts
• Manual: reproduce session with tool-drop + assistant cargo-cult; confirm UI shows no stacked leading numbers on new completions
• Manual: confirm 99 files… / numbered-list user text is preserved after transform

Closes #97

Greptile Summary

This PR fixes two related failures caused by a mismatch between how Magic Context tags are injected at the transform layer and stripped at the persistence boundary. It introduces stripPersistedAssistantText as a shared pipeline (whole §N§ pair removal, malformed hybrid removal, stray § cleanup, then trim) consumed by both OpenCode's text-complete.ts and Pi's strip-tag-prefix.ts, and updates hasMeaningfulPart to run stripTagPrefix before emptiness checks so tag-only ghost messages are pruned after tool drops.

• Ghost message fix: hasMeaningfulPart now calls stripTagPrefix before .trim().length > 0, correctly treating a part whose text is only §424§ (or malformed §15298\">§15298§) as empty and removing the message.
• Persistence boundary: stripPersistedAssistantText removes whole §N§ pairs globally (not bare § characters), eliminating digit residue that previously survived global §-only stripping and stacked on re-injection passes.
• Transform layer preserved: stripTagPrefix and prependTag still only strip leading §-shaped notation, explicitly preserving legitimate leading digits (99 files…, 2024 roadmap, numbered lists).

Confidence Score: 5/5

Safe to merge; changes are narrowly scoped to tag-stripping helpers and the emptiness check in hasMeaningfulPart, all guarded by updated unit tests.

The ghost-message fix in hasMeaningfulPart is minimal and the logic is straightforward. The new stripPersistedAssistantText pipeline replaces duplicate inline regexes in two places with a well-tested shared function. The transform-layer strip (stripTagPrefix) is deliberately unchanged for legitimate-digit preservation. Prior review concerns (trailing-space residue, missing byteSize/isThinkingPart tests, JSDoc placement) are all addressed in this revision.

No files require special attention.

Important Files Changed

Filename	Overview
packages/plugin/src/hooks/magic-context/tag-content-primitives.ts	Adds stripPersistedAssistantText (4-step pipeline) plus helper exports and a multi-pass loop in stripTagPrefix. Implementation is correct and well-reasoned.
packages/plugin/src/hooks/magic-context/tool-drop-target.ts	Core fix: hasMeaningfulPart now calls stripTagPrefix before checking trimmed length, correctly identifying tag-only ghost messages as empty.
packages/plugin/src/hooks/magic-context/text-complete.ts	Replaces two-step inline strip with a call to stripPersistedAssistantText, centralising persistence-boundary logic.
packages/pi-plugin/src/strip-tag-prefix.ts	Simplified to a thin wrapper over stripPersistedAssistantText, removing 60+ lines of duplicated logic.
packages/plugin/src/hooks/magic-context/temporal-awareness.ts	Refactors inline tag-prefix peeling to use peelLeadingMcTagNotation, now also handling malformed prefixes.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[Assistant completion] -->|text| B[stripPersistedAssistantText]
    B --> B1["1. Strip leading well-formed runs"]
    B1 --> B2["2. Remove all complete pairs globally"]
    B2 --> B3["3. Remove malformed hybrids globally"]
    B3 --> B4["4. Remove stray section signs"]
    B4 --> B5["5. trim()"]
    B5 --> C[Clean persisted text]
    D["Tool drop hasMeaningfulPart"] -->|text part| E[stripTagPrefix leading only]
    E --> F{empty after trim?}
    F -- yes --> G[Remove ghost message]
    F -- no --> H[Keep message]

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