feat: hippocampal memory system, improved tool/subagent error messages, YOLO mode cleanup

[cy2311]

This PR contains four fixes/features across two branches of work:

Bug Fixes

1. YOLO mode verbosity (#2922)

Added "Do not announce or restate the current mode between actions — just execute." to the YOLO mode prompt to suppress repeated mode announcements before each tool call.

2. Tool error message clarity (#2657)

Removed generic suffixes from format_tool_error() when the underlying error already explains the cause (mode restriction, shell access, etc.), so the agent can tell exactly why a tool is unavailable.

3. Subagent session name conflicts (#2656)

Added elapsed time (started Xs ago) to the session-name-conflict error message, so the agent can distinguish between a running agent, a completed one, or a stale session.

Feature

4. Hippocampal Memory System (#2935)

New crates/memory/ crate with SQLite-backed structured memory store:

• entities table: Files, PRs, issues, concepts, decisions
• relations table: Directed edges with kind + strength (e.g. dispatch.rs ── part_of ──▶ PR #2933)
• facts table: Standalone statements with FTS5 full-text search for pattern-completion queries
• memorize tool: Agent stores a structured fact with importance score and optional entity binding
• recall tool: Agent queries memory by keyword, gets facts + related entities + graph relationships
• Active forgetting: prune_low_importance_facts() removes old/low-value facts
• Lazy-initialized on first engine context build via memory_db_path in EngineConfig

Files Changed

Cargo.toml                                   |   1 +
crates/memory/Cargo.toml                     |  19 ++
crates/memory/src/lib.rs                     |  29 +++
crates/memory/src/schema.rs                  |  80 +++++++
crates/memory/src/store.rs                   | 390 +++++++++++++++++++
crates/tui/Cargo.toml                        |   1 +
crates/tui/src/core/engine.rs                |  29 +-
crates/tui/src/core/engine/tool_setup.rs     |   5 +
crates/tui/src/main.rs                       |   6 +
crates/tui/src/prompts/modes/yolo.md         |   2 +
crates/tui/src/tools/memorize.rs             | 105 +++++++
crates/tui/src/tools/mod.rs                  |   2 +
crates/tui/src/tools/recall.rs               | 165 +++++++++
crates/tui/src/tools/registry.rs             |  16 +
crates/tui/src/tools/spec.rs                 |   6 +
crates/tui/src/tools/subagent/mod.rs         |   9 +-
crates/tui/src/core/engine/dispatch.rs       |  15 +-
crates/tui/src/tui/ui.rs                     |   6 +
18 files changed, 882 insertions(+), 4 deletions(-)

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[github-actions]

Thanks @cy2311 for taking the time to contribute.

This repository is observing a maintainer-managed PR intake gate in dry-run mode, so this pull request is staying open. This note helps maintainers prepare the allowlist before any enforcement is considered.

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[gemini-code-assist]

Code Review

This pull request updates the YOLO mode prompt markdown file by adding an instruction to execute actions directly without announcing or restating the current mode. It also changes the header level from H2 to H5. The reviewer recommends keeping the H2 header level to maintain consistency with other mode prompts.

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[gemini-code-assist]

The header level was changed from ## (H2) to ##### (H5). To maintain consistency with other mode prompts (such as ## Mode: Agent and ## Mode: Plan) and to keep a clean hierarchy in the composed system prompt, it is recommended to keep this as an H2 header.

Suggested change

	##### Mode: YOLO
	## Mode: YOLO

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[Hmbown]

@cy2311 — thank you, there's a lot of good work here. We'd like to take it, but in pieces, because it bundles two very different kinds of change:

The three fixes are wanted now. The YOLO-mode announcement suppression (#2922), the format_tool_error() clarity fix (#2657), and the subagent name-conflict elapsed-time message (#2656) are all small, reviewable, and address open milestone bugs. Please split them into one (or three) small PRs against current main and we'll merge promptly. Note #2951 just landed a related prompt note telling the model not to announce modes — your yolo.md line is complementary, just rebase over it.

The memory crate needs a design conversation first. A new crates/memory/ SQLite+FTS5 store with memorize/recall tools is an architectural decision that overlaps two existing tracks: the memory Phase 3 epic (#534) and the WhaleFlow external-memory design (docs/WHALEFLOW_EXTERNAL_MEMORY.md). Rather than merge a third memory architecture, let's reconcile on #2935 (your design issue): if accepted it would land opt-in/feature-flagged and coordinated with those tracks. Your entity/relation/fact schema with active forgetting is a genuinely interesting shape — we want the discussion, not to lose it.

Closing nothing here — this PR can stay open as the reference while the split PRs land.