feat: sqlite session storage (#6594)

This PR:

- Adds retainedTail to compaction entries in the new agent harness so we don't have to walk up the tree for the 2000 tokens before compaction,
- Changes getPathToRoot to getPathToRootOrCompaction to only load until last compaction, as unnecessary to access all nodes where it is called,
- Adds a SQLite storage backend, in a separate packages/session-backend-sqlite, with a migration system and schemas as per on-site discussions: sessions to match session header messages (except for metadata, which I couldn't understand what it's used for or where it gets written, so I omitted it), session_entries for shared entry types as columns plus payload as a json for what remains, session_sequences to represent the append-only, serialized nature of the jsonl files, branch_entries to attribute nodes to branches (relationship one-to-many), and session_materialized with the session info (see /session in TUI) to act as a "cache" or quick-access for costs, message count, token info, labels, session name, and model-thinking-level config (e.g. for fast resume).
- This is compatible with the new agent harness Session abstraction.

packages/coding-agent/install-lock/package-lock.json

@@ -638,9 +638,6 @@
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-				"glibc"
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 		"node_modules/@mariozechner/clipboard-linux-arm64-musl": {
@@ -657,9 +654,6 @@
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-			"libc": [
-				"musl"
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 		"node_modules/@mariozechner/clipboard-linux-riscv64-gnu": {
@@ -676,9 +670,6 @@
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 				"riscv64"
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-			"libc": [
-				"glibc"
-			],
 			"optional": true
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 		"node_modules/@mariozechner/clipboard-linux-x64-gnu": {
@@ -695,9 +686,6 @@
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 				"x64"
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-			"libc": [
-				"glibc"
-			],
 			"optional": true
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 		"node_modules/@mariozechner/clipboard-linux-x64-musl": {
@@ -714,9 +702,6 @@
 			"cpu": [
 				"x64"
 			],
-			"libc": [
-				"musl"
-			],
 			"optional": true
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 		"node_modules/@mariozechner/clipboard-win32-arm64-msvc": {
@@ -790,7 +775,8 @@
 			"license": "Apache-2.0",
 			"engines": {
 				"node": ">=8.0.0"
-			}
+			},
+			"peer": true
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 		"node_modules/@opentelemetry/semantic-conventions": {
 			"version": "1.41.1",
@@ -1834,7 +1820,8 @@
 			"license": "MIT",
 			"funding": {
 				"url": "https://github.com/sponsors/colinhacks"
-			}
+			},
+			"peer": true
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 		"node_modules/zod-to-json-schema": {
 			"version": "3.25.2",